1.1What’s electromagnetic radiation- a sinusoidal electric and magnetic wave traveling through the space- a discrete series of “particles” that have a specific energy but have no mass, photons

Both. Wave-particle duality!

1.2 Wave properties of electromagnetic radiation(considering electric field only since it’s responsible for spectroscopy including transmission, reflection, refraction, and absorption): wavelength, linear distance between two equivalent points on successive waves.A: amplitude, the length of electric vector at a maximum: frequency, the number of oscillations occurred per sec.T: period, time for 1 to pass a fixed point, =1/

y = A sin(t + ), with time as variable

: angular velocity =2,

: phase angle

Coherent: a set of waves with identical and difference in phase angle remains constant

y = A sin(t + ),

y’ = A’sin(t + ’), - ’ = constantFig. 6-1 (p.133)

1.2.1 Transmissionvelocity of wave propagation (m/s) = (m) x (s-1)

- In a vacuum: electromagnetic wave travels at the speed of light, c = 3.00 x108 m/s

- In other media, remains constant, and thus v decreases v = c/n,

n: the medium refractive index 1.00

1.2.2 Reflection and refraction

The fraction of reflection:

The extent of refraction:

1

2

2

1

sinsin

nn

212

212

)()(

nnnn

II

incident

reflection

1.2.3 DiffractionParallel electromagnetic wave can be bend when passing through a narrow opening (width ).

Fig. 6-7 (p.138)

Fig. 6-7 (p.138) Fig. 6-8 (p.139)

Two diffracted rays from two slits will have interference. Constructive interference (intense band) can be observed when the difference in path length from two slits is equal to wavelength (first order interference), or 2, 3 … corresponding to difference between two phase angles = 2n, n is an integral 1,2,3…

2.1Particle Properties

According to Photoelectric Effect experiment (p144-146)

energy of a photon can be related to its frequency

E (J) = hh: Planck's constant, 6.6254 x10-34 Js

=c/ E = hc/energy is inversely proportional to the wavelength

2.2Some Commonly Used Units wavelength units vary with the spectral regionX-ray and short UV: Å = 10-10 m

UV/Visible range: nm = 10-9 mm = 10-6 m

Infrared range: mwavenumber (cm-1):

Photon energyX-ray region: eV 1J = 6.24 x1018 eVVisible region: kJ/mol kJ/mol = J/photon x6.02 x1023 photon/mol X10-3 kJ/J

)(/1)( 1 cmcm

2.2 Range of wavelength/frequencies

Fig. 6-3 and Table 6-1 (p.135)

3.1Postulates of Quantum Mechanics- Atoms, ions and molecules exist in discrete energy states only -- quantized

E0: groundE1, E2, E3 … : excited statesExcitation can be electronic, vibrational or rotationalEnergy levels of atoms, ions or molecules are all different,Measuring energy levels gives means of identification of chemical species – spectroscopy

- When an atom, ion or molecule changes energy state, it absorbs or emits radiation with energy equal to the energy difference

E = E1 - E0

The wavelength or frequency of radiation absorbed or emitted during a transition

hchE

hEhcE//

3.2 Emission Spectra from Excited States

Fig. 6-21 (p.151)

Fig. 6-15 (p.147) Sample is excited by the application of thermal, electrical or chemical energy

Fig. 6-23 (p.153)

Measurement of the emitted radiation as a function of wavelength

3.3Absorption Spectra

Just as in emission spectra an atom, ion or molecule can only absorb radiation if energy matches separation between two energy states.

AtomsNo vibrational or rotation energy levels – sharp line spectra with few featuresNa 3s3p 589.0, 589.6 nm (yellow),

For valence excitation, visible energyFor core(inner) excitation, UV and X-ray energy

Fig. 6-23 (p.153)

Measurement of the amount of light absorbed as a function of wavelength

3s3p 589.0, 589.6 nm

Fig. 6-16 (p.148) For absorption to occur, the energy of incident beam must be correspond to one of the energy difference

MoleculesElectronic, vibrational and rotational energy levels all involved –

Each electronic state – many vibratioanl statesEach vibrational states – many rotational states

E = Eelec + Evib + Erot

broad band spectra with many features.

Fig. 6-23 (p.153)

3.4Relaxation Processes

Lifetime of excited state is short (fsms) – relaxation processes

Nonradiative relaxationloss of energy by collisions, happens in a series of small steps.Tiny temperature rise of surrounding species

Radiative relaxation (emission)Fluorescence (<10-5s)

Stokes shift: emission has a lower frequency than the radiation (due to vibrational relaxation occurs before fluorescence).

Fig. 6-24 (p.154)

E2-E1

E2+e4”-E1

Fast vibrational relaxation

Stokes shift: emission has a lower frequency than the radiation due to vibrational relaxation occurs before fluorescence.

3.5 Quantitative aspects of spectrochemical measurementsAssuming blank signal is already corrected for

Emission Spectra

S = kc

Absorption Spectra

Transmittance expressed as percent: T% = P/P0 x 100%

Absorbance: A = -log10 T = log(P0/P)

Beer’s LawA = bc: molar absorptivity (Lmol-1cm-1)b: path length of absorption (cm-1)C: molar concentration (mol L-1)

Fig. 6-25 (p.158)