Assistant of the pharmaceutical chemistry department

Burmas Nataliya Ivanivnae-mail: Natashenka-Burmas@rambler.ru

Spectroscopy: theory, classification,

application

PLANPLAN

1. 1. Essence of spectroscopic methods of Essence of spectroscopic methods of analysis.analysis.

2. The main characteristics of 2. The main characteristics of electromagnetic radiation.electromagnetic radiation.

3. Classification of spectroscopic methods 3. Classification of spectroscopic methods of analysis.of analysis.

4. Utilizing spectroscopy in analysis.4. Utilizing spectroscopy in analysis.

1. 1. Essence of spectroscopic methods of Essence of spectroscopic methods of analysis.analysis.

The spectroscopic methods of The spectroscopic methods of analysis are based on cooperating of analysis are based on cooperating of the electromagnetic radiation with a the electromagnetic radiation with a substance.substance.

2. The main characteristics of electromagnetic 2. The main characteristics of electromagnetic radiation.radiation.

The electromagnetic radiationThe electromagnetic radiation is described is described based on:based on:

a)a) the wave‘s nature of lightthe wave‘s nature of light (break of a (break of a light , scattering, diffraction, refraction of light , scattering, diffraction, refraction of a light);a light);

b)b) the corpuscular nature of a lightthe corpuscular nature of a light (absorption and emanation of a light by (absorption and emanation of a light by meals - quantum).meals - quantum).

Electromagnetic radiationElectromagnetic radiation (often abbreviated (often abbreviated E-E-M radiationM radiation or or EMREMR) is a phenomenon that takes ) is a phenomenon that takes the form of self-propagating waves in a vacuum or the form of self-propagating waves in a vacuum or in in a a matter. It consists of electric and magnetic matter. It consists of electric and magnetic field components which oscillate in phase field components which oscillate in phase perpendicular to each other and perpendicular to perpendicular to each other and perpendicular to the direction of energy propagation. the direction of energy propagation.

The characteristic of electromagnetic radiation as a wave:

a) the wave's length is a spatial period of a wave – the distance over which the wave's shape repeats;;

b) a b) a ffrequencyrequency is the number of is the number of occurrences of a repeating event per unit occurrences of a repeating event per unit timetime;;

c) the c) the wwavenaven's nnumberumber is is the number of the number of wavelengths per unit distance, that is, 1/λ wavelengths per unit distance, that is, 1/λ where λ=where λ= wavelengthwavelength

~

TThe concept was expanded greatly to comprise he concept was expanded greatly to comprise any measurement of a quantity as a function of any measurement of a quantity as a function of either wavelength or frequency. Thus it also can either wavelength or frequency. Thus it also can refer to a response to an alternating field or refer to a response to an alternating field or varying frequency (varying frequency (νν). A further extension of the ). A further extension of the scope of the definition added energy (scope of the definition added energy (EE) as a ) as a variable, once the very close relationship variable, once the very close relationship EE = = hνhν for for photons photons was realized (was realized (hh is the Planck is the Planck constant).constant).

hh = 6,6262 = 6,6262··1010-34-34 JJ·· ss с = 2,9979 с = 2,9979 ··101088 MM ·s·s-1-1

~hchc

hE

Electromagnetic spectrumElectromagnetic spectrum

Absorption energy occurs at the excitation Absorption energy occurs at the excitation elementary systems (nuclear, atomic, molecular) elementary systems (nuclear, atomic, molecular) and move her to a lower energic level to a higher and move her to a lower energic level to a higher level.level.

Electromagnetic radiationElectromagnetic radiation is classified into is classified into several types according to the frequency of its several types according to the frequency of its wave; these types include (in order of increasing wave; these types include (in order of increasing frequency and decreasing wavelength): frequency and decreasing wavelength):

a)a) radio waves, radio waves, b)b) microwaves, microwaves, c)c) terahertz radiation, terahertz radiation, d)d) infrared radiation, infrared radiation, e)e) visible light, visible light, f)f) ultraviolet radiation, ultraviolet radiation, g)g) X-raysX-raysh)h) gamma rays. gamma rays.

A A spectrumspectrum is a condition that is not is a condition that is not limited to a specific set of values but can limited to a specific set of values but can vary infinitely within a continuum.vary infinitely within a continuum.

The The electromagnetic spectrumelectromagnetic spectrum is the range is the range of all possible frequencies of electromagnetic of all possible frequencies of electromagnetic radiationradiation.. The "electromagnetic spectrum" of The "electromagnetic spectrum" of an object is the characteristic distribution of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed electromagnetic radiation emitted or absorbed by that particular object. by that particular object.

The sThe spectrum of absorptionpectrum of absorption

The intensity of the absorption varies as a The intensity of the absorption varies as a function of frequency, and this variation function of frequency, and this variation is the absorption spectrum. is the absorption spectrum.

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1000 2000 3000 4000

Wavenumbers (cm-1)

TypeTypess of spectrums of spectrums::

1)1) radiation (emission spectroscopy)radiation (emission spectroscopy)

2)2) absorption (absoabsorption (absoptption spectroscopy)ion spectroscopy)

3)3) reflection (spectroscopy of reflection)reflection (spectroscopy of reflection)

4)4) dispersion (IR spectroscopy)dispersion (IR spectroscopy)

5)5) luminescence (luminescent spectroscopy)luminescence (luminescent spectroscopy)

3.Classification of spectroscopic methods of analysis.3.Classification of spectroscopic methods of analysis.

The type of spectroscopy depends on the physical quantity measured. Normally, the quantity that is measured is an intensity, either of energy absorbed or produced.

I. Nature of excitation measured:1. Electromagnetic spectroscopy involves interaction of

matter with electromagnetic radiation, such as light. 2. Electron spectroscopy involves interaction with electron

beams. 3. Dielectric spectroscopy involves the frequency of an

external electrical field. 4. Mechanical spectroscopy involves the frequency of an

external mechanical stress, e.g. a torsion applied to a piece of material.

II. II. Along with that distinction, they can be Along with that distinction, they can be classified on the nature of their interaction:classified on the nature of their interaction:

1.1. Absorption spectroscopyAbsorption spectroscopy uses the range of the uses the range of the electromagnetic spectra in which a substance electromagnetic spectra in which a substance absorbs. absorbs.

2.2. Emission spectroscopyEmission spectroscopy uses the range of uses the range of electromagnetic spectra in which a substance electromagnetic spectra in which a substance radiates (emits). The substance first must absorb radiates (emits). The substance first must absorb energy. This energy can be from a variety of energy. This energy can be from a variety of sources, which determines the name of the sources, which determines the name of the subsequent emission, like subsequent emission, like luminescenceluminescence. .

3.3. Scattering spectroscopyScattering spectroscopy measures the amount of measures the amount of light that a substance scatters at certain light that a substance scatters at certain wavelengths, incident angles, and polarization wavelengths, incident angles, and polarization angles. angles.

MethodMethod Description of energy‘s quantum

Process

Radiofrequency (YAMR, EPR)

Microwave

Optical:

a) UPh

b) Visible

Infra-red (ICh,

CD)

X-ray photography

Gamma-radiation (kernel-physical)

101-10-1 m

10-1-10-3 m

10-200-400 nm400-760 nm

760-106 nm10-13000 сm-1

10-2-10 nm

10-4-10-1 nm

Change of spins kernels and electrons

Change of rotatory states

Change states of valency electrons

Change swaying states

Change of the state of internal electrons

Nuclear reactions

Rotational spectroscopyRotational spectroscopy or or microwave microwave spectroscopyspectroscopy studies the absorption and emission studies the absorption and emission of electromagnetic radiation (typically in the of electromagnetic radiation (typically in the microwave region of the electromagnetic spectrum) microwave region of the electromagnetic spectrum) by molecules associated with a corresponding by molecules associated with a corresponding change in the rotational quantum number of the change in the rotational quantum number of the molecule. The use of microwaves in spectroscopy molecule. The use of microwaves in spectroscopy essentially became possible due to the development essentially became possible due to the development of microwave technology for RADAR during of microwave technology for RADAR during World War II. Rotational spectroscopy is only World War II. Rotational spectroscopy is only really practical in the gas phase where the really practical in the gas phase where the rotational motion is quantized. In solids or liquids rotational motion is quantized. In solids or liquids the rotational motion is usually quenched due to the rotational motion is usually quenched due to collisions. collisions.

Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system. It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the phonon modes in the system.

Fluorescence spectroscopy is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light of a lower energy, typically, but not necessarily, visible light. A complementary technique is absorption spectroscopy.

X-ray absorption spectroscopy (XAS) is a widely-used technique for determining the local geometric and/or electronic structure of matter. The experiment is usually performed at synchrotron radiation sources, which provide intense and tunable X-ray beams. Samples can be in the gas-phase, solution, or condensed matter (ie. solids).

4. Utilizing spectroscopy in analysis4. Utilizing spectroscopy in analysis

Spectrums used both for Spectrums used both for qualitative qualitative analysis and analysis and also for also for quantitativequantitative analysis. analysis.

The The qualitative analysisqualitative analysis is the position (energy, is the position (energy, frequency, length of wave, wavefrequency, length of wave, wave‘s‘s number) of number) of maximums (lines) in the electromagnetic maximums (lines) in the electromagnetic spectrum.spectrum.

Quantitative analysis is Quantitative analysis is anan intensity intensity (amplitude) of spectral line is the function (amplitude) of spectral line is the function of concentration substance. To use such of concentration substance. To use such description of spectral line, which straight description of spectral line, which straight proportional the concentration of a proportional the concentration of a substance.substance.

For example, optical density:For example, optical density:

lCA

Spectroscopy/spectrometry is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them.

Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler shift of their spectral lines.

Spectroscopy is the use of the absorption, emission, or Spectroscopy is the use of the absorption, emission, or scattering of electromagnetic radiation by matter to scattering of electromagnetic radiation by matter to qualitatively or quantitatively study the matter or to study qualitatively or quantitatively study the matter or to study physical processes. physical processes. Absorption:Absorption: A transition from a lower level to a higher A transition from a lower level to a higher level with transfer of energy from the radiation field to an level with transfer of energy from the radiation field to an absorber, atom, molecule, or solid. absorber, atom, molecule, or solid.

Emission:Emission: A transition from a higher level to a lower level A transition from a higher level to a lower level with transfer of energy from the emitter to the radiation with transfer of energy from the emitter to the radiation field. If no radiation is emitted, the transition from higher to field. If no radiation is emitted, the transition from higher to lower energy levels is called nonradiative decay. lower energy levels is called nonradiative decay.

Scattering:Scattering: Redirection of light due to its interaction with Redirection of light due to its interaction with matter. Scattering might or might not occur with a transfer matter. Scattering might or might not occur with a transfer of energy, i.e., the scattered radiation might or might not of energy, i.e., the scattered radiation might or might not have a slightly different wavelength compared to the light have a slightly different wavelength compared to the light incident on the sample. incident on the sample.