photo chemistry 4

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Photochemistry, a sub-discipline of chemistry, is the study of the interactionsbetween light and atomsor molecules.[1]Photochemistry describes chemicalreactionsthat proceed with the absorption of light. Everyday examples includephotosynthesis, the degradation of plastics and the formation of vitamin withsunlight.

Principles

Light is a type of electromagnetic radiation,a source of energy. The GrotthussDraper law(forchemists Theodor Grotthussand John W. Draper), states that light must e asored y a

chemical sustance in order for aphotochemical reactionto ta!e place.

The second law of photochemistry, the "tar!#$instein law, states that for each photon of light

asored y a chemical system, only one molecule is acti%ated for a photochemical reaction.This law, also !nown as thephotoe&ui%alence law, was deri%ed y 'lert $insteinat the time

when the &uantum (photon) theoryof light was eing de%eloped.

hemical reactions occur only when a molecule is pro%ided the necessary acti%ation energy. '

simple e*ample can e the comustionof gasoline(ahydrocaron) into caron dio*ide andwater. +n this reaction, the acti%ation energy is pro%ided in the form of heat or a spar!. +n case of

photochemical reactions light pro%ides the acti%ation energy. "implistically, light is one

mechanism for pro%iding the acti%ation energy re&uired for many reactions. +f laser light isemployed, it is possile to selecti%ely e*cite a molecule so as to produced a desired electronic

and %irational state. $&ually, the emission from a particular state may e selecti%ely monitored,

pro%iding a measure of the population of that state. +f the chemical system is at low pressure, thisenales scientists to oser%e the energy distriution of the products of a chemical reaction efore

the differences in energy ha%e een smeared out and a%eraged y repeated collisions.

The asorption of a photon of light y a reactant molecule may also permit a reaction to occur

not ust y ringing the molecule to the necessary acti%ation energy, ut also y changing thesymmetry of the molecule-s electronic configuration, enaling an otherwise inaccessile reaction

path, as descried y the Woodward#offmann selection rules. ' /0/ cycloaddition reaction is

one e*ample of apericyclic reactionthat can e analy1ed using these rules or y the related

frontier molecular oritaltheory.

2hotochemical reactions in%ol%e electronic reorgani1ation initiated y electromagnetic radiation.

The reactions are se%eral orders of magnitude faster than thermal reactions3 reactions as fast as

4567seconds and associated processes as fast as 45648seconds are often oser%ed.

Spectral regions

2hotochemists typically wor! in only a few sections of the electromagnetic spectrum. "ome of

the most widely used sections, and their wa%elengths, are the following9

:ltra%iolet9 455;55 nm


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>ear infrared9 =55/855 nm

Applications

?any important processes in%ol%e photochemistry. The premier e*ample isphotosynthesis,in

which most plants use solar energy to con%ert caron dio*ideand water into glucose, disposingof o*ygenas a side#product. umans rely on photochemistry for the formation of %itamin D. +n

fireflies,an en1ymein the adomen cataly1es a reaction that results inioluminescence.@/A

2hotochemistry can also e highly destructi%e. ?edicine ottles are often made with dar!enedglass to pre%ent the drugs from photodegradation. ' per%asi%e reaction is the generation of

singlet o*ygen y photosensiti1ed reactions of triplet o*ygen. Typical photosensiti1ers include

tetraphenylporphyrinand methylene lue.The resulting singlet o*ygen is an aggressi%e o*idant,capale of con%erting # onds into #B groups.+nphotodynamic therapy, light is used to

destroy tumors y the action of singlet o*ygen.

?any polymeri1ations are started yphotoinitiatiors,which decompose upon asoring light toproduce the free radicals for Cadical polymeri1ation.

+n the area of photochemistry, a photochemical reactionis a chemical reactionthat is inducedy light. 2hotochemical reactions are %aluale in organicand inorganic chemistryecause theyproceed differently than thermal reactions. 2hotochemical reactions are not only %ery useful ut

also can e a serious nuisance, as in the photodegradation of many materials, e.g.poly%inyl

chloride.' large#scale application of photochemistry isphotoresisttechnology, used in theproduction of microelectroniccomponents.


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"chlen! tuecontaining slurry of orange crystals of Ee/(B)7in acetic acid after itsphotochemical synthesis from Ee(B)8. Themercury lamp(connected to white power cords) can

e seen on the left, set inside a water#ac!eted &uart1 tue.

The emitted light must of course reach the targeted functional groupwithout eing loc!ed y

the reactor, medium, or other functional groups present. Eor many applications, &uart1is used forthe reactors as well as to contain the lamp.2yre*asors at wa%elengths shorter than /=8 nm.

The sol%ent is an important e*perimental parameter. "ol%ents are potential reactants and for this

reason, chlorinated sol%ents are a%oided ecause the #l ond can lead to chlorinationof thesustrate. "trongly asoring sol%ents pre%ent photons from reaching the sustrate. ydrocaron

sol%ents asor only at short wa%elengths and are thus preferred for photochemical e*periments

re&uiring high energy photons. "ol%ents containing unsaturation asor at longer wa%elengthsand can usefully filter out short wa%elengths. Eor e*ample,cyclohe*aneand acetonecut off

(asor strongly) at wa%elengths shorter than /48 and 5 nm, respecti%ely.

Excitation

2hotoe*citationis the first step in a photochemical process where the reactant is ele%ated to astate of higher energy, ane*cited state.The photon can e asored directly y the reactant or y

aphotosensiti1ers, which asors the photon and transfers the energy to the reactant. The

opposite process is called &uenchingwhen a photoe*ited state is deacti%ated y a chemicalreagent.

?ost photochemical transformations occur through a series of simple steps !nown as primary

photochemical processes. Bne common e*ample of these processes is the e*cited state proton

transfer ($"2T).
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Organic photochemistry

$*amples of photochemical organic reactionsare electrocyclic reactions,photoisomeri1ationand

>orrish reactions.

'l!enesundergo many important reactions that proceed %ia a photon#induced F to F transition.The first electronic e*cited state of an al!ene lac! the F#ond, so that rotation aout the #

ond is rapid and the molecule engages in reactions not oser%ed thermally. These reactions

include cis#trans isomeri1ation, cycloaddition to other (ground state) al!ene to gi%e cycloutanederi%ati%es. The cis#trans isomeri1ation of a (poly)al!ene is in%ol%ed in retinal, a component of

the machinery of %ision. The dimeri1ation of al!enes is rele%ant to the photodamage of D>',

where thymine dimersare oser%ed upon illuminating D>' to :< radiation. "uch dimersinterfere with transcription. The eneficial effects of sunlight are associated with the

photochemically induced retro#cycli1ation (decycli1ation) reaction of ergosterolto gi%e%itamin

D. +n the De?ayo reaction, an al!ene reacts with a 4,#di!etone reacts %ia itsenolto yield a 4,8#di!etone. "till another common photochemical reaction is Himmerman-s Di#pi#methane

rearrangement.

+n an industrial application, aout 455,555 tonnes ofen1yl chlorideare prepared annually y the

gas#phase photochemical reaction oftoluenewith chlorine.@;AThe light is asored y chlorinemolecule, the low energy of this transition eing indicted y the yellowish color of the gas. The

photon induces homolysis of the l#l ond, and the resulting chlorine radical con%erts toluene

to the en1yl radical9

l/0 hI / lK80 lK 8/K 0 l

8/K 0 lK 8/l

?ercaptanscan e produced y photochemical addition ofhydrogen sulfide(/") to alpha

olefins.

Inorganic and organometallic photochemistry

oordination comple*esand organometallic compoundsare also photoreacti%e. These reactions

can entail cis#trans isomeri1ation. ?ore commonly photoreactions result in dissociation of

ligands, since the photon e*cites an electron on the metal to an orital that is antionding withrespect to the ligands. Thus, metal caronylsthat resist thermal sustitution undergo

decaronylation upon irradiation with :< light. :


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History

'lthough leaching has long een practiced, the first photochemical reaction was descried y

Trommsdorf in 4M;.@8Ae oser%ed that crystalsof the compound N#santoninwhen e*posed tosunlightturned yellow and urst. +n a /55= study the reaction was descried as a succession of

three steps ta!ing place within a single crystal.@A

The first step is a rearrangement reactionto a cyclopentadienoneintermediate 2, the second one adimeri1ationin a Diels#'lder reaction(3) and the third one a intramolecular@/0/Acycloaddition

(4). The ursting effect is attriuted to a large change in crystal %olume on dimeri1ation.

Reerences

4. !+:2',Compendium of Chemical Terminology, /nd ed. (the Gold Ooo!) (477=). Bnlinecorrected %ersion9 (/55#) photochemistry.

/. !Da%id "tanley "aunders +nsect cloc!s, $lse%ier, /55/,+"O> 5;;;85;5=7p. 4=7

. !hristophe Duga%eis#trans isomeri1ation in iochemistry,Wiley#


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2atric! ?carren, U. >. ou!, and ?iguel '. Garcia#Gariay J. 'm. hem. "oc.,"2$(/), 7M; #7M;=,2%%&. doi945.45/4Sa5=4M7o

See also

ournal of Photochemistry and Photo!iology 2hotoelectrochemical cell

Photochemical and Photo!iological Sciences

Photochemistry and Photo!iology

2hotochemical Logic Gates

2hotosynthesis

Photoelectrochemical processesusually involve transforming light into otherforms of energy.[1]!hese processes apply to photochemistry, optically pumpedlasers, sensiti"ed solar cells, luminescence, and the e#ect of reversible change ofcolor upon exposure to light. !o the right photonsare emitted in a coherentbeamfrom a laser

Electron excitation

$fter absorbing energy, an electron may %ump from the ground state to a higherenergy excited state.

Electron excitationis the mo%ement of an electronto a higher energy state. This can either edone y photoe*citation (2$), where the original electron asors the photon and gains all the

photon-s energy or y electricale*citation($$), where the original electron asors the energy of

another, energetic electron. Within a semiconductor crystal lattice, thermal e*citation is a processwhere lattice %irations pro%ide enough energy to mo%e electrons to a higher energy and. When
http://en.wikipedia.org/wiki/J._Am._Chem._Soc.http://en.wikipedia.org/wiki/J._Am._Chem._Soc.http://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1021%2Fja073189ohttp://dx.doi.org/10.1021%2Fja073189ohttp://en.wikipedia.org/wiki/Journal_of_Photochemistry_and_Photobiologyhttp://en.wikipedia.org/wiki/Photoelectrochemical_cellhttp://en.wikipedia.org/wiki/Photochemical_and_Photobiological_Scienceshttp://en.wikipedia.org/wiki/Photochemistry_and_Photobiologyhttp://en.wikipedia.org/wiki/Photochemical_Logic_Gateshttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-photochemelec-process-0http://en.wikipedia.org/wiki/Photonshttp://en.wikipedia.org/wiki/Coherence_(physics)http://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Energy_statehttp://en.wikipedia.org/wiki/Excited_statehttp://en.wikipedia.org/wiki/Excited_statehttp://en.wikipedia.org/wiki/Energy_bandhttp://en.wikipedia.org/wiki/File:Energylevels.pnghttp://en.wikipedia.org/wiki/File:Energylevels.pnghttp://en.wikipedia.org/wiki/J._Am._Chem._Soc.http://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1021%2Fja073189ohttp://en.wikipedia.org/wiki/Journal_of_Photochemistry_and_Photobiologyhttp://en.wikipedia.org/wiki/Photoelectrochemical_cellhttp://en.wikipedia.org/wiki/Photochemical_and_Photobiological_Scienceshttp://en.wikipedia.org/wiki/Photochemistry_and_Photobiologyhttp://en.wikipedia.org/wiki/Photochemical_Logic_Gateshttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-photochemelec-process-0http://en.wikipedia.org/wiki/Photonshttp://en.wikipedia.org/wiki/Coherence_(physics)http://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Energy_statehttp://en.wikipedia.org/wiki/Excited_statehttp://en.wikipedia.org/wiki/Energy_band


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an e*cited electron falls ac! to a lower energy state again, it is called electron rela*ation. This

can e done y radiation of a photon or gi%ing the energy to a third spectator particle as well. @/A

+n physics there is a specific technical definition forenergy le%elwhich is often associated withan atom eing e*cited to an e*cited state. The e*cited state, in general, is in relation to the

ground state, where the e*cited state is at a higher energy le%elthan the ground state.

Photoexcitation

Photoexcitationis the mechanism of electron e*citationyphotonasorption, when the energyof the photon is too low to causephotoioni1ation. The asorption of photon ta!es place in

accordance to the 2lanc!-s Vuantum Theory.

2hotoe*citation plays role in photoisomeri1ation. 2hotoe*citation is e*ploited indye#sensiti1ed

solar cells,photochemistry, luminescence,opticallypumpedlasers, and in somephotochromicapplications.

See also: Photoelectric efect

Photoisomeri'ation

+n chemistry,photoisomeri'ationis moleculareha%ior in which structural change etween

isomersis caused y photoe*citation. Ooth re%ersile and irre%ersile photoisomeri1ation

reactions e*ist. owe%er, the word photoisomeri1ation usually indicates a re%ersile process.

2hotoisomeri1ale molecules are already put to practical use, for instance, inpigmentsforrewritale Ds, D


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photon minus the electron inding energyof the state it left. 2hotons with energies less than the

electron inding energy may e asored or scatteredut will not photoioni1e the atom or ion. @A

Eor e*ample, to ioni1e hydrogen,photons need an energy greater than 4. electron%olts, whichcorresponds to a wa%elength of 74./ nm.@;AEor photons with greater energy than this, the energy

of the emitted photoelectron is gi%en y9

where his 2lanc!-s constantand $is the fre&uencyof the photon.

This formula defines thephotoelectric effect.

>ot e%ery photon which encounters an atom or ion will photoioni1e it. The proaility of

photoioni1ation is related to thephotoioni1ation cross#section, which depends on the energy of

the photon and the target eing considered. Eor photon energies elow the ioni1ation threshold,the photoioni1ation cross#section is near 1ero. Out with the de%elopment of pulsed lasers it has

ecome possile to create e*tremely intense, coherent light where multi#photon ioni1ation mayoccur. 't e%en higher intensities (around 4548# 454WScm/of infrared or %isile light), non#

perturati%ephenomena such as !arrier suppression ioni%ation@8Aand rescattering ioni%ation@A

are oser%ed.

[edit] Multi-photon ionization

"e%eral photons of energy elow the ioni1ation threshold may actually comine their energies to

ioni1e an atom. This proaility decreases rapidly with the numer of photons re&uired, ut the

de%elopment of %ery intense, pulsed lasers still ma!es it possile. +n the perturati%e regime(elow aout 454;WScm/at optical fre&uencies), the proaility of asoring&photons depends

on the laser#light intensity'as'&.@=A

'o%e#threshold ioni1ation ('T+) @MAis an e*tension of multi#photon ioni1ation where e%en more

photons are asored than actually would e necessary to ioni1e the atom. The e*cess energygi%es the released electron higher!inetic energythan the usual case of ust#ao%e threshold

ioni1ation. ?ore precisely, The released electron will ha%e an integer numer of photon#energies

more !inetic energy than in the normal (lowest possile numer of photons) ioni1ation.

&ee also

Main articles: Fluorescence spectroscopy, Fluorescence, and Photoionization

mode

Photo-(em)er

Main article: Photo-Dember
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+n semiconductor physics the 2hoto#Demereffect (named after its disco%erer . Demer)

consists in the formation of a charge dipolein the %icinity of a semiconductorsurface after ultra#

fastphoto#generationof charge carriers. The dipole forms owing to the difference of moilities(or diffusion constants) for holes and electrons which comined with the rea! of symmetry

pro%ided y the surface lead to an effecti%e charge separation in the direction perpendicular to

the surface.@7A

*rotthuss+(raper la,

The *rotthuss+(raper la,(also called 2rinciple of 2hotochemical 'cti%ation) states that only

that light which is asored y a system can ring aout a photochemical change. ?aterials such

as dyes and phosphors must e ale to asor light at optical fre&uencies. ' asis forEluorescence and phosphorescence is found in this law. +t was first proposed in 4M4= y Theodor

Grotthussand John W. Draper. This is considered to e one of the two asic laws of

photochemistry. The second law is the"tar!$instein law, which says that primary chemical orphysical reactions occur with each photon asored.@45A

Star+Einstein la,

The Star+Einstein la,is named after the German#orn physicists Johannes "tar!and'lert

$instein, who independently formulated the law etween 475M and 474. +t is !nown also as the

photochemical e.ui/alence la,or photoe.ui/alence la,. +n essence it says that e%ery photon

that is asored will cause a (primary) chemical or physical reaction.@44A

The photon is a &uantum of radiation, or one unit of radiation. Therefore, this is a single unit of

$? radiation that is e&ual to 2lanc!-s constant (h) times the fre&uency of light. This &uantity is

symoli1ed y

The photochemical e&ui%alence law is also restated as follows9 for e%ery moleof a sustance that

reacts, an e&ui%alent mole of &uanta of light are asored. The formula is9@44A

"molX&AhI

where >'is '%ogadro-s numer.

The photochemical e&ui%alence law applies to the part of a light#induced reaction that is referred

to as the primary process (i.e.asorptionor fluorescence).@44A

+n most photochemical reactions the primary process is usually followed y so#called secondary

photochemical processes that are normal interactions etween reactants not re&uiring asorption

of light. 's a result such reactions do not appear to oey the one &uantumone molecule reactant

relationship.@44A

The law is further restricted to con%entional photochemical processes using light sources with

moderate intensities3 high#intensity light sources such as those used in flash photolysisand in
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laser e*periments are !nown to cause so#called iphotonic processes3 i.e., the asorption y a

molecule of a sustance of two photons of light.@44A

A)sorption 0electromagnetic radiation1

(ain article:A!sorption )electromagnetic radiation*

+nphysics, a)sorptionof electromagnetic radiation is the way y which the energyof aphoton

is ta!en up y matter, typically the electrons of an atom. Thus, the electromagnetic energy is

transformed to other forms of energy, for e*ample, to heat. The asorption of light during wa%epropagationis often calledattenuation. :sually, the asorption of wa%es does not depend on their

intensity (linear asorption), although in certain conditions (usually, in optics), the medium

changes its transparency dependently on the intensity of wa%es going through, and the"aturaleasorption(or nonlinear asorption) occurs.

Photosensiti'ation2hotosensiti1ation is a process of transferring the energyof asored light. 'fter asorption, the

energy is transferred to the (chosen) reactants. This is part of the wor! ofphotochemistryingeneral. +n particular this process is commonly employed where reactions re&uire light sources of

certain wa%elengthsthat are not readily a%ailale.@4/A

Eor e*ample, mercuryasors radiation at 4M;7 and /8=angstroms, and the source is often

high#intensity mercury lamps.+t is a commonly used sensiti1er. When mercury %apor is mi*edwith ethylene, and the compound is irradiatedwith a mercury lamp, this results in the

photodecomposition of ethylene to acetylene. This occurs on asorption of light to yield e*cited

state mercury atoms, which are ale to transfer this energy to the ethylene molecules, and are inturn deacti%ated to their initial energy state.@4/A

admium3 some of the nole gases,for e*ample (usually)*enon3 1inc3en1ophenone3 and a

large numer of organic dyes, are also used as sensiti1ers.@4/A

2hotosensitisers are a !ey component ofphotodynamic therapyused to treat cancers.

Sensiti'er

+Sensiti%er+ redirects here, or the particulate material used to create voids that aid in the

initiation or propagation of an e.plosive/s detonation 0ave1 see".plosive sensitiser,

' sensiti'erin chemoluminescenceis a chemical compound, capale oflight emissionafter it

has recei%ed energy from a molecule, which ecame e*cited pre%iously in the chemical reaction.' good e*ample is this9

When an al!aline solution ofsodium hypochloriteand a concentrated solution of hydrogen

pero*ideare mi*ed, a reaction occurs9
http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-StarkEinsteinlaw-10http://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Attenuation_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Attenuation_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Saturable_absorptionhttp://en.wikipedia.org/wiki/Saturable_absorptionhttp://en.wikipedia.org/wiki/Saturable_absorptionhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Reactanthttp://en.wikipedia.org/wiki/Photochemistryhttp://en.wikipedia.org/wiki/Photochemistryhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Photosensitization-11http://en.wikipedia.org/wiki/Mercury_(element)http://en.wikipedia.org/wiki/Mercury_(element)http://en.wikipedia.org/wiki/Angstromhttp://en.wikipedia.org/wiki/Angstromhttp://en.wikipedia.org/wiki/Arc_lamphttp://en.wikipedia.org/wiki/Arc_lamphttp://en.wikipedia.org/wiki/Ethylenehttp://en.wikipedia.org/wiki/Irradiatedhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Photosensitization-11http://en.wikipedia.org/wiki/Cadmiumhttp://en.wikipedia.org/wiki/Noble_gaseshttp://en.wikipedia.org/wiki/Noble_gaseshttp://en.wikipedia.org/wiki/Xenonhttp://en.wikipedia.org/wiki/Xenonhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Benzophenonehttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Photosensitization-11http://en.wikipedia.org/wiki/Photodynamic_therapyhttp://en.wikipedia.org/wiki/Explosive_sensitiserhttp://en.wikipedia.org/wiki/Chemoluminescencehttp://en.wikipedia.org/wiki/Light_emissionhttp://en.wikipedia.org/wiki/Light_emissionhttp://en.wikipedia.org/wiki/Light_emissionhttp://en.wikipedia.org/wiki/Sodium_hypochloritehttp://en.wikipedia.org/wiki/Sodium_hypochloritehttp://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-StarkEinsteinlaw-10http://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Attenuation_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Saturable_absorptionhttp://en.wikipedia.org/wiki/Saturable_absorptionhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Reactanthttp://en.wikipedia.org/wiki/Photochemistryhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Photosensitization-11http://en.wikipedia.org/wiki/Mercury_(element)http://en.wikipedia.org/wiki/Angstromhttp://en.wikipedia.org/wiki/Arc_lamphttp://en.wikipedia.org/wiki/Ethylenehttp://en.wikipedia.org/wiki/Irradiatedhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Photosensitization-11http://en.wikipedia.org/wiki/Cadmiumhttp://en.wikipedia.org/wiki/Noble_gaseshttp://en.wikipedia.org/wiki/Xenonhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Benzophenonehttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Photosensitization-11http://en.wikipedia.org/wiki/Photodynamic_therapyhttp://en.wikipedia.org/wiki/Explosive_sensitiserhttp://en.wikipedia.org/wiki/Chemoluminescencehttp://en.wikipedia.org/wiki/Light_emissionhttp://en.wikipedia.org/wiki/Sodium_hypochloritehttp://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Hydrogen_peroxide


11/27

lB#(a&) 0 /B/(a&) B/(g) 0 0(a&) 0 l#(a&) 0 B#(a&)

B/is e*cited o*ygen # meaning, one or more electrons in the B/molecule ha%e een promoted

to higher#energy molecular oritals. ence, o*ygen produced y this chemical reaction somehow-asored- the energy released y the reaction and ecame e*cited. This energy state is unstale,

therefore it will return to the ground statey lowering its energy. +t can do that in more than oneway9

it can react further, without any light emission

it can lose energy without emission, for e*ample, gi%ing off heat to the surroundings or

transferring energy to another molecule

it can emit light

The intensity, duration and color of emitted light depend on &uantumand !ineticalfactors.

owe%er, e*cited molecules are fre&uently less capale of light emission in terms of rightness

and duration when compared to sensiti1ers. This is ecause sensiti1ers can store energy (that is,

e e*cited) for longer periods of time than other e*cited molecules. The energy is stored throughmeans of &uantum %iration, so sensiti1ers are usually compounds which either include systems

of aromaticrings or many conugated doule and tripleondsin their structure. ence, if an

e*cited molecule transfers its energy to a sensiti1er thus e*citing it, longer and easier to &uantifylight emission is often oser%ed.

The color (that is, the wa%elength), rightness and duration of emission depend upon the

sensiti1er used. :sually, for a certain chemical reaction, many different sensiti1ers can e used.

ist o some common sensiti'ers


12/27

luorescence spectroscopya!a fluorometry or spectrofluorometry, is a type of electromagnetic

spectroscopywhich analy1es fluorescencefrom a sample. +t in%ol%es using a eam of light,

usually ultra%iolet light, that e*cites the electrons inmoleculesof certain compounds and causesthem to emit light of a lower energy, typically, ut not necessarily, %isile light. '

complementary techni&ue is asorption spectroscopy.@4A@4;A

De%ices that measurefluorescenceare calledfluorometersor fluorimeters.

A)sorption spectroscopy

(ain article:A!sorption spectroscopy

A)sorption spectroscopyrefers tospectroscopictechni&ues that measure the asorption of

radiation, as a function of fre&uency or wa%elength, due to its interaction with a sample. The

sample asors energy, i.e., photons, from the radiating field. The intensity of the asorption%aries as a function of fre&uency, and this %ariation is the asorption spectrum. 'sorption

spectroscopy is performed across the electromagnetic spectrum.@4A@4;A

See also

$lectron inding energy

+someri1ation

2hotoioni1ation mode

2hotochromism

2hotoelectric effect

2hotoioni1ation detector

Reerences

4. !"chia%ello, ?ario3 >'TB (47M8#5/).Photoelectrochemistry1 Photocatalysis and Photoreactors

undamentals and 2evelopments. "pringer London, Limited. pp. 7.+"O>7=M75/==47;4.

http9SSoo!s.google.comSYidXrLC?e24UGhsZpgX2C7Zd&X2hotoelectrochemical0processes[%XonepageZ&X2hotoelectrochemica

l\/5processesZfXfalse.

/. !?adden, C.2.3 odling, U (478#5/). Two electron states in elium.Astrophysical ournal

"4"9 ;.Oicode478'pJ...4;4..;?. doi945.45MS4;M4/

. ]abCadiation."ncyclop3dia 4ritannica Online. 2hotoelectric. eect. /557. pp. 4.

http9SSwww.ritannica.comS$Ochec!edStopicS;MM85=Sradiation .Cetrie%ed /557#44#57.

;. !arroll, O. W.3 Bstlie, D. '. (/55=). An 'ntroduction to (odern Astrophysics. London9 'ddison#

Wesley. p. 4/4.+"O>5/4;;/M;7.

8. !http9SSwww.iop.orgS$JSastractS45#=M7S;4S8SC5
http://en.wikipedia.org/wiki/Electromagnetic_spectroscopyhttp://en.wikipedia.org/wiki/Electromagnetic_spectroscopyhttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Ultraviolet_lighthttp://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Absorption_spectroscopyhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Modern-spectroscopy-12http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Modern-spectroscopy-12http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-sym-spectroscopy-13http://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Fluorometerhttp://en.wikipedia.org/wiki/Fluorometerhttp://en.wikipedia.org/wiki/Absorption_spectroscopyhttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Absorption_spectrumhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Modern-spectroscopy-12http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-sym-spectroscopy-13http://en.wikipedia.org/wiki/Electron_binding_energyhttp://en.wikipedia.org/wiki/Isomerizationhttp://en.wikipedia.org/wiki/Photoionization_modehttp://en.wikipedia.org/wiki/Photochromismhttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Photoionization_detectorhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-photochemelec-process_0-0http://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/9789027719461http://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-2-electron_1-0http://en.wikipedia.org/wiki/Bibcodehttp://en.wikipedia.org/wiki/Bibcodehttp://adsabs.harvard.edu/abs/1965ApJ...141..364Mhttp://adsabs.harvard.edu/abs/1965ApJ...141..364Mhttp://en.wikipedia.org/wiki/Digital_object_identifierhttp://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1086%2F148132http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-1http://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-3http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0321442849http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-4http://www.iop.org/EJ/abstract/1063-7869/41/5/R03http://www.iop.org/EJ/abstract/1063-7869/41/5/R03http://en.wikipedia.org/wiki/Electromagnetic_spectroscopyhttp://en.wikipedia.org/wiki/Electromagnetic_spectroscopyhttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Ultraviolet_lighthttp://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Absorption_spectroscopyhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Modern-spectroscopy-12http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-sym-spectroscopy-13http://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Fluorometerhttp://en.wikipedia.org/wiki/Absorption_spectroscopyhttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Absorption_spectrumhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-Modern-spectroscopy-12http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_note-sym-spectroscopy-13http://en.wikipedia.org/wiki/Electron_binding_energyhttp://en.wikipedia.org/wiki/Isomerizationhttp://en.wikipedia.org/wiki/Photoionization_modehttp://en.wikipedia.org/wiki/Photochromismhttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Photoionization_detectorhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-photochemelec-process_0-0http://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/9789027719461http://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://books.google.com/?id=rLRMeP1KGhsC&pg=PR9&dq=Photoelectrochemical+processes#v=onepage&q=Photoelectrochemical%20processes&f=falsehttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-2-electron_1-0http://en.wikipedia.org/wiki/Bibcodehttp://adsabs.harvard.edu/abs/1965ApJ...141..364Mhttp://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1086%2F148132http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photoionisation-1_2-1http://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-3http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0321442849http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-4http://www.iop.org/EJ/abstract/1063-7869/41/5/R03


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. !http9SSieee*plore.ieee.orgSstampSstamp.spYarnumerX548;7;

=. !Deng, H3 $erly, J (?arch 47M8). ?ultiphoton asorption ao%e ioni1ation threshold y

atoms in strong laser fields., Opt, Soc, Am, 42()9 ;74.http9SSprola.aps.orgSastractS2CLS%;/Si4=Sp44/=4.

M. !'gostini, 23 Eare, E3 ?ainfray, G3 2etite, G3 Cahman, > U (/ 'pril 47=7).Eree#Eree

Transitions Eollowing "i*#2hoton +oni1ation of ^enon 'toms.Phys, Rev, Lett,42(4=)9 44/=445.doi945.445S2hysCe%Lett.;/.44/= . http9SSprola.aps.orgSastractS2CLS%;/Si4=Sp44/=4.

7. !De!orsy, T.3 'uer, .3 Oa!!er, . J.3 Cos!os, . G.3 Uur1, . (477). T1 electromagneticemission y coherent infrared#acti%e phonons.Physical Revie0 43(=)9 ;558.

doi945.445S2hysCe%O.8.;558 .

45. !Cadiation."ncyclop3dia 4ritannica Online. radiation. 0physics15 Photochemistry. /557.pp. 4. http9SSwww.ritannica.comS$Ochec!edStopicS;MM85=Sradiation.Cetrie%ed /557#44#57.

44. ]abcde2hotoe&ui%alence law."ncyclop3dia 4ritannica Online. /557#44

4/. ]abc2hotosensiti1ation."ncyclop3dia 4ritannica, 5667,. Online. /557. pp. 4.

http9SSwww.ritannica.comS$Ochec!edStopicS;8M48Sphotosensiti1ation.Cetrie%ed /557#44#45.

4. ]ab?odern "pectroscopy (2aperac!) y J. ?ichael ollas +"O> 5;=5M;;4=

4;. ]ab"ymmetry and "pectroscopy9 'n +ntroduction to 5;M4;;^
http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-5http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01549346http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01549346http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-6http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-7http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1103%2FPhysRevLett.42.1127http://dx.doi.org/10.1103%2FPhysRevLett.42.1127http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-photodember_8-0http://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1103%2FPhysRevB.53.4005http://dx.doi.org/10.1103%2FPhysRevB.53.4005http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Grotthuss.E2.80.93Draper-law_9-0http://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-2http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-2http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-3http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-4http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-4http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-2http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-2http://www.britannica.com/EBchecked/topic/458153/photosensitizationhttp://www.britannica.com/EBchecked/topic/458153/photosensitizationhttp://www.britannica.com/EBchecked/topic/458153/photosensitizationhttp://www.britannica.com/EBchecked/topic/458153/photosensitizationhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-1http://en.wikipedia.org/wiki/Special:BookSources/0470844167http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-1http://en.wikipedia.org/wiki/Special:BookSources/048666144Xhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-5http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01549346http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-6http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-7http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1103%2FPhysRevLett.42.1127http://prola.aps.org/abstract/PRL/v42/i17/p1127_1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-photodember_8-0http://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1103%2FPhysRevB.53.4005http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Grotthuss.E2.80.93Draper-law_9-0http://www.britannica.com/EBchecked/topic/488507/radiationhttp://www.britannica.com/EBchecked/topic/488507/radiationhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-2http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-3http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-StarkEinsteinlaw_10-4http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-1http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Photosensitization_11-2http://www.britannica.com/EBchecked/topic/458153/photosensitizationhttp://www.britannica.com/EBchecked/topic/458153/photosensitizationhttp://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-Modern-spectroscopy_12-1http://en.wikipedia.org/wiki/Special:BookSources/0470844167http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-0http://en.wikipedia.org/wiki/Photoelectrochemical_processes#cite_ref-sym-spectroscopy_13-1http://en.wikipedia.org/wiki/Special:BookSources/048666144X


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Electromagnetic radiation(often are%iated E-6 radiationor E6R) is a form of energye*hiiting wa%e#li!e eha%ior as it tra%els through space. $?C has oth electricandmagnetic

fieldcomponents, which oscillatein phase perpendicular to each other and perpendicular to the

direction of energypropagation.

$lectromagnetic radiation is classified according to the fre&uencyof its wa%e. +n order ofincreasing fre&uency and decreasing wa%elength,these areradio wa%es, microwa%es,infrared

radiation, %isile light, ultra%iolet radiation,^#raysandgamma rays(see $lectromagnetic

spectrum). Theeyesof %arious organismssense a small and somewhat %ariale window offre&uencies called the%isile spectrum. Thephotonis the &uantum of the electromagnetic

interaction and the asic unit of light and all other forms of electromagnetic radiation and is

also the force carrierfor the electromagnetic force.

$? radiation carries energyandmomentumthat may e imparted to matterwith which it

interacts.

Theory

&hows the relative wavelengths of the electromagnetic waves of three di#erent

colors of light'blue, green and red( with a distance scale in micrometres along the

x-axis.

Main article: Maxwell's euations

James ler! ?a*wellfirst formally postulated electromagnetic ,a/es. These were suse&uently

confirmed y einrich ert1. ?a*well deri%ed a wa%e form of the electric and magnetice&uations, thus unco%ering the wa%e#li!e nature of electric and magnetic fields, and their

symmetry. Oecause the speed of $? wa%es predicted y the wa%e e&uation coincided with the

measured speed of light,?a*well concluded that lightitself is an $? wa%e.
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'ccording to ?a*well-s e&uations, a time#%arying electric fieldgenerates a time#%arying

magnetic fieldand vice versa. Therefore, as an oscillating electric field generates an oscillating

magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. Theseoscillating fields together form a propagating electromagnetic wa%e.

'&uantum theoryof the interaction etween electromagnetic radiation and matter such aselectrons is descried y the theory of&uantum electrodynamics.

[edit] Properties

Electromagnetic waves can be imagined as a self-propagating transverse oscillatingwave of electric and magnetic )elds. !his diagram shows a plane linearly polari"ed

wave propagating from right to left. !he electric )eld is in a vertical plane and the

magnetic )eld in a hori"ontal plane.

Thephysicsof electromagnetic radiation is electrodynamics.$lectromagnetismis the physicalphenomenon associated with the theory of electrodynamics. $lectric and magnetic fields oey

the properties of superposition.Thus, a field due to any particular particle or time#%arying

electric or magnetic field contriutes to the fields present in the same space due to other causes.Eurther, as they are %ectorfields, all magnetic and electric field %ectors add together according to

%ector addition. Eor e*ample, in optics two or more coherent lightwa%es may interact and y

constructi%e or destructi%e interference yield a resultant irradiance de%iating from the sum of thecomponent irradiances of the indi%idual lightwa%es.

"ince light is an oscillation it is not affected y tra%elling through static electric or magnetic

fields in a linear medium such as a %acuum. owe%er in nonlinear media, such as somecrystals,

interactions can occur etween light and static electric and magnetic fields _ these interactionsinclude the Earaday effectand the Uerr effect.

+n refraction, a wa%e crossing from one medium to another of different densityalters its speed

and direction upon entering the new medium. The ratio of the refracti%e indices of the media

determines the degree of refraction, and is summari1ed y "nell-s law. Light disperses into a

%isile spectrumas light passes through a prism ecause of the wa%elength dependent refracti%einde* of the prism material (Dispersion).

$? radiation e*hiits oth wa%e properties andparticleproperties at the same time (see wa%e#

particle duality). Ooth wa%e and particle characteristics ha%e een confirmed in a large numerof e*periments. Wa%e characteristics are more apparent when $? radiation is measured o%er

relati%ely large timescales and o%er large distances while particle characteristics are more e%ident

when measuring small timescales and distances. Eor e*ample, when electromagnetic radiation is
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asored y matter, particle#li!e properties will e more o%ious when the a%erage numer of

photons in the cue of the rele%ant wa%elength is much smaller than 4. :pon asorption of light,

it is not too difficult to e*perimentally oser%e non#uniform deposition of energy. "trictlyspea!ing, howe%er, this alone is not e%idence of particulate eha%ior of light, rather it reflects

the &uantum nature of matter.@4A

There are e*periments in which the wa%e and particle natures of electromagnetic wa%es appear in

the same e*periment, such as the self#interference of a singlephoton. Truesingle#photone*periments (in a &uantum optical sense) can e done today in undergraduate#le%el las.@/AWhen

a single photon is sent through an interferometer, it passes through oth paths, interfering with

itself, as wa%es do, yet is detected y aphotomultiplieror other sensiti%e detector only once.

[edit] Wave model

$lectromagnetic radiation is atrans%erse wa%emeaning that the oscillations of the wa%es are

perpendicular to the direction of energy transfer and tra%el. 'n important aspect of the nature of

light is fre&uency. The fre&uency of a wa%e is its rate of oscillation and is measured in hert1, the"+unit of fre&uency, where one hert1 is e&ual to one oscillation per second. Light usually has a

spectrum of fre&uencies which sum together to form the resultant wa%e. Different fre&uenciesundergo different angles of refraction.

' wa%e consists of successi%e troughs and crests, and the distance etween two adacent crests or

troughs is called the wa%elength. Wa%es of the electromagnetic spectrum %ary in si1e, from %ery

long radio wa%es the si1e of uildings to %ery short gamma rays smaller than atom nuclei.Ere&uency is in%ersely proportional to wa%elength, according to the e&uation9

where vis the speed of the wa%e (cin a %acuum, or less in other media), fis the fre&uency and `

is the wa%elength. 's wa%es cross oundaries etween different media, their speeds change uttheir fre&uencies remain constant.

+nterferenceis the superposition of two or more wa%es resulting in a new wa%e pattern. +f the

fields ha%e components in the same direction, they constructi%ely interfere, while opposite

directions cause destructi%e interference.

The energy in electromagnetic wa%es is sometimes called radiant energy.

[edit] Particle modelSee also: !uantization "physics#and !uantum optics

Oecause energy of an $? interaction is &uanti1ed, $? wa%es are emitted and asored as

discrete pac!ets of energy, or &uanta, calledphotons.@AOecause photons are emitted and

asored y charged particles, they act as transporters of energy, and are associated with wa%eswith fre&uency proportional to the energy carried. The energy perphotoncan e related to the

fre&uency %ia the 2lanc!$instein e&uation9@;A
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where"is the energy, his 2lanc!-s constant, andfis fre&uency. The energy is commonly

e*pressed in the unitof electron%olt(e


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fre&uency of the wa%e gi%en y2lanc!-srelation" 8 h$, where"is the energy of the photon, h

X ./ 456;JKs is 2lanc!-s constant,and $is the fre&uency of the wa%e.

Bne rule is always oeyed regardless of the circumstances9 $? radiation in a %acuum alwaystra%els at the speed of light, relative to the o!server, regardless of the oser%er-s %elocity. (This

oser%ation led to 'lert $instein-s de%elopment of the theory of special relati%ity.)

+n a medium (other than %acuum), %elocity factororrefracti%e inde*are considered, depending

on fre&uency and application. Ooth of these are ratios of the speed in a medium to speed in a%acuum.

7hermal radiation and electromagnetic radiation as a orm

o heat

Main article: &hermal radiation

The asic structure of matterin%ol%es charged particles ound together in many different ways.

When electromagnetic radiation is incident on matter, it causes the charged particles to oscillateand gain energy. The ultimate fate of this energy depends on the situation. +t could e

immediately re#radiated and appear as scattered, reflected, or transmitted radiation. +t may also

get dissipated into other microscopic motions within the matter, coming to thermal e&uiliriumand manifesting itself as thermal energyin the material. With a few e*ceptions such as

fluorescence, harmonic generation,photochemical reactionsand thephoto%oltaic effect,

asored electromagnetic radiation simply deposits its energy y heating the material. This

happens oth for infrared and non#infrared radiation. +ntense radio wa%es can thermally urnli%ing tissue and can coo! food. +n addition to infrared lasers, sufficiently intense %isile and

ultra%iolet lasers can also easily set paper afire. +oni1ing electromagnetic radiation can createhigh#speed electrons in a material and rea! chemical onds, ut after these electrons collidemany times with other atoms in the material e%entually most of the energy gets downgraded to

thermal energy, this whole process happening in a tiny fraction of a second. That infrared

radiation is a form of heat and other electromagnetic radiation is not, is a widespreadmisconceptionin physics.Anyelectromagnetic radiation can heat a material when it is asored.

The in%erse or time#re%ersed process of asorption is responsile for thermal radiation. ?uch of

the thermal energy in matter consists of random motion of charged particles, and this energy can

e radiated away from the matter. The resulting radiation may suse&uently e asored yanother piece of matter, with the deposited energy heating the material. Cadiationis an important

mechanism of heat transfer.

The electromagnetic radiation in an opa&ue ca%ity at thermal e&uilirium is effecti%ely a form of

thermal energy, ha%ing ma*imumradiation entropy. The thermodynamic potentialsofelectromagnetic radiation can e well#defined as for matter. Thermal radiation in a ca%ity has

energy density (see2lanc!-s Law) of
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Differentiating the ao%e with respect to temperature, we may say that the electromagneticradiation field has an effecti%e %olumetric heat capacitygi%en y

Electromagnetic spectrum

Main article: lectroma%netic spectrum

Electromagnetic spectrumwith light highlighted
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Legend:

* + amma rays

+ ard -rays

& + &oft -/ays

E0 + Extreme ultraviolet

20 + 2ear ultraviolet

isible light

23/ + 2ear infrared

43/ + 4oderate infrared

53/ + 5ar infrared

adio !aves:

E5 + Extremely high fre6uency'4icrowaves(

&5 + &uper high fre6uency'4icrowaves(05 + 0ltrahigh fre6uency

5 + ery high fre6uency

5 + igh fre6uency

45 + 4edium fre6uency

75 + 7ow fre6uency

75 + ery low fre6uency
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5 + oice fre6uency

075 + 0ltra low fre6uency

&75 + &uper low fre6uency

E75 + Extremely low fre6uency

Generally, $? radiation (the designation -radiation- e*cludes static electric and magnetic andnear fields) is classified y wa%elength intoradio,microwa%e,infrared, the %isile regionwe

percei%e as light, ultra%iolet, ^#raysand gamma rays.'ritrary electromagnetic wa%es can

always e e*pressed y Eourier analysisin terms of sinusoidal monochromatic wa%es which cane classified into these regions of the spectrum.

The eha%ior of $? radiation depends on its wa%elength. igher fre&uencies ha%e shorter

wa%elengths, and lower fre&uencies ha%e longer wa%elengths. When $? radiation interacts with

single atoms and molecules, its eha%ior depends on the amount of energy per &uantum it carries."pectroscopycan detect a much wider region of the $? spectrum than the %isile range of

;55 nm to =55 nm. ' common laoratory spectroscope can detect wa%elengths from / nm to

/855 nm. Detailed information aout the physical properties of oects, gases, or e%en stars cane otained from this type of de%ice. +t is widely used inastrophysics. Eor e*ample, hydrogen

atomsemitradio wa%esof wa%elength/4.4/ cm.

Sound,a/es are not electromagnetic radiation8't the lower end of the electromagnetic

spectrum, aout /5 1 to aout /5 !1, are fre&uencies that might e considered in the audiorange. owe%er, electromagnetic wa%es cannot e directly percei%ed y human ears. "ound

wa%es are the oscillating compression of molecules. To e heard, electromagnetic radiation must

e con%erted to air pressure wa%es, or if the ear is sumerged, water pressure wa%es.

[edit] Light

Main article: (i%ht

$? radiation with a wa%elengthetween appro*imately ;55 nmand =55 nm is directly detectedy the human eyeand percei%ed as %isile light. Bther wa%elengths, especially neary infrared

(longer than =55 nm) and ultra%iolet (shorter than ;55 nm) are also sometimes referred to as

light, especially when %isiility to humans is not rele%ant.

+f radiation ha%ing a fre&uency in the %isile region of the $? spectrum reflects off of an oect,

say, a owl of fruit, and then stri!es our eyes, this results in our %isual perceptionof the scene.

Bur rain-s %isual system processes the multitude of reflected fre&uencies into different shades

and hues, and through this not#entirely#understood psychophysical phenomenon, most people

percei%e a owl of fruit.

't most wa%elengths, howe%er, the information carried y electromagnetic radiation is not

directly detected y human senses. >atural sources produce $? radiation across the spectrum,

and our technologycan also manipulate a road range of wa%elengths. Bptical fiertransmitslight which, although not suitale for direct %iewing, can carry data that can e translated into

sound or an image. To e meaningful oth transmitter and recei%er must use some agreed#upon
http://en.wikipedia.org/wiki/Voice_frequencyhttp://en.wikipedia.org/wiki/Ultra_low_frequencyhttp://en.wikipedia.org/wiki/Super_low_frequencyhttp://en.wikipedia.org/wiki/Extremely_low_frequencyhttp://en.wikipedia.org/wiki/Near_and_far_fieldhttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/Gamma_rayshttp://en.wikipedia.org/wiki/Gamma_rayshttp://en.wikipedia.org/wiki/Fourier_analysishttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Astrophysicshttp://en.wikipedia.org/wiki/Astrophysicshttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Emission_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Centimetrehttp://en.wikipedia.org/w/index.php?title=Electromagnetic_radiation&action=edit&section=9http://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Human_eyehttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Visual_perceptionhttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Voice_frequencyhttp://en.wikipedia.org/wiki/Ultra_low_frequencyhttp://en.wikipedia.org/wiki/Super_low_frequencyhttp://en.wikipedia.org/wiki/Extremely_low_frequencyhttp://en.wikipedia.org/wiki/Near_and_far_fieldhttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/Gamma_rayshttp://en.wikipedia.org/wiki/Fourier_analysishttp://en.wikipedia.org/wiki/Spectroscopyhttp://en.wikipedia.org/wiki/Astrophysicshttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Emission_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Centimetrehttp://en.wikipedia.org/w/index.php?title=Electromagnetic_radiation&action=edit&section=9http://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Human_eyehttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Visual_perceptionhttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Optical_fiber


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encoding system # especially so if the transmission is digital as opposed to the analog nature of

the wa%es.

[edit] adio !aves

Main article: )adio wa*es

Cadio wa%es can e made to carry information y %arying a comination of the amplitude,fre&uency and phase of the wa%e within a fre&uency and.

When $? radiation impinges upon aconductor, it couples to the conductor, tra%els along it, and

inducesan electric current on the surface of that conductor y e*citing the electrons of the

conducting material. This effect (thes!in effect) is used in antennas. $? radiation may alsocause certain molecules to asor energy and thus to heat up3 this is e*ploited in microwa%e

o%ens. Cadio wa%es are notioni1ing radiation, as the energy per photon is too small.

(eri/ation

!his article8s toneor style may not "e appropriate for Wi#ipedia.

&peci)c concerns may be found on the tal9 page. &ee :i9ipedia8s guide to

writing better articlesfor suggestions. "+pril .#

$lectromagnetic wa%es as a general phenomenon were predicted y the classical laws ofelectricityand magnetism, !nown as?a*well-s e&uations. +nspection of ?a*well-s e&uations

without sources (charges or currents) results in, along with the possiility of nothing happening,

nontri%ial solutions of changing electric and magnetic fields. Oeginning with ?a*well-se&uations in free space9

where

is a vector di#erential operator 'see el(.

Bne solution,

,
http://en.wikipedia.org/w/index.php?title=Electromagnetic_radiation&action=edit&section=10http://en.wikipedia.org/wiki/Radio_waveshttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Radio_frequency_inductionhttp://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Microwave_ovenhttp://en.wikipedia.org/wiki/Microwave_ovenhttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/Wikipedia:TONEhttp://en.wikipedia.org/wiki/Talk:Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Wikipedia:Guide_to_writing_better_articleshttp://en.wikipedia.org/wiki/Wikipedia:Guide_to_writing_better_articleshttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Delhttp://en.wikipedia.org/w/index.php?title=Electromagnetic_radiation&action=edit&section=10http://en.wikipedia.org/wiki/Radio_waveshttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Radio_frequency_inductionhttp://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Microwave_ovenhttp://en.wikipedia.org/wiki/Microwave_ovenhttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/Wikipedia:TONEhttp://en.wikipedia.org/wiki/Talk:Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Wikipedia:Guide_to_writing_better_articleshttp://en.wikipedia.org/wiki/Wikipedia:Guide_to_writing_better_articleshttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Del


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is tri%ial.

Eor a more useful solution, we utili1e %ector identities, which wor! for any %ector, as follows9

To see how we can use this, ta!e the curl of e&uation (/)9

$%aluating the left hand side9

where we simpli)ed the above by using e6uation '1(.

$%aluate the right hand side9

$&uations () and (=) are e&ual, so this results in a %ector#%alued differential e&uationfor the

electric field, namely

'pplying a similar pattern results in similar differential e&uation for the magnetic field9

.

These differential e&uations are e&ui%alent to the wa%e e&uation9

where

c;is the speed of the wave in free space and
http://en.wikipedia.org/wiki/List_of_vector_identitieshttp://en.wikipedia.org/wiki/Differential_equationhttp://en.wikipedia.org/wiki/Wave_equationhttp://en.wikipedia.org/wiki/List_of_vector_identitieshttp://en.wikipedia.org/wiki/Differential_equationhttp://en.wikipedia.org/wiki/Wave_equation


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$describes a displacement

Br more simply9

where is d8$lembertianotice that in the case of the electric and magnetic fields, the speed is9

Which, as it turns out, is the speed of lightin %acuum. ?a*well-s e&uations ha%e unified the

%acuum permitti%ityb5, the%acuum permeaility5, and the speed of light itself, c5. Oefore thisderi%ation it was not !nown that there was such a strong relationshipetween light andelectricity and magnetism.

Out these are only two e&uations and we started with four, so there is still more information

pertaining to these wa%es hidden within ?a*well-s e&uations. Let-s consider a generic %ectorwa%e for the electric field.

ere is the constant amplitude,fis any second differentiale function, is a unit %ector in the

direction of propagation, and is a position %ector. We oser%e that is ageneric solution to the wa%e e&uation. +n other words

,

for a generic wa%e tra%eling in the direction.

This form will satisfy the wa%e e&uation, ut will it satisfy all of ?a*well-s e&uations, and with

what corresponding magnetic fieldY
http://en.wikipedia.org/wiki/D'Alembert_operatorhttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Vacuum_permittivityhttp://en.wikipedia.org/wiki/Vacuum_permeabilityhttp://en.wikipedia.org/wiki/Vacuum_permeabilityhttp://en.wikipedia.org/wiki/Vacuum_permeabilityhttp://en.wikipedia.org/wiki/Electromagnetic_wave_equationhttp://en.wikipedia.org/wiki/D'Alembert_operatorhttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Vacuum_permittivityhttp://en.wikipedia.org/wiki/Vacuum_perm

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