Spectroscopy:
theory, classification,
application
Assistant of the
pharmaceutical chemistry department
Burmas Nataliya Ivanivna
e-mail: Natashenka-Burmas@rambler.ru
PLAN
1. Essence of spectroscopic methods of
analysis.
2. The main characteristics of
electromagnetic radiation.
3. Classification of spectroscopic methods
of analysis.
4. Utilizing spectroscopy in analysis.
1. Essence of spectroscopic methods of
analysis.
The spectroscopic methods of
analysis are based on cooperating of
the electromagnetic radiation with a
substance.
2. The main characteristics of electromagnetic
radiation.
The electromagnetic radiation is described
based on:
a) the wave‘s nature of light (break of a
light , scattering, diffraction, refraction of
a light);
b) the corpuscular nature of a light
(absorption and emanation of a light by
meals - quantum).
Electromagnetic radiation (often abbreviated EM radiation or EMR) is a phenomenon that takes
the form of self-propagating waves in a vacuum or
in a matter. It consists of electric and magnetic field
components which oscillate in phase perpendicular
to each other and perpendicular to 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 frequency  is the number of
occurrences of a repeating event per unit
time;
c) the waven's number ~ is the number of
wavelengths per unit distance, that is, 1/λ
where λ= wavelength
The concept was expanded greatly to comprise
any measurement of a quantity as a function of
either wavelength or frequency. Thus it also can
refer to a response to an alternating field or
varying frequency (ν). A further extension of the
scope of the definition added energy (E) as a
variable, once the very close relationship E = hν
for photons was realized (h is the Planck
constant).
E  h 


h = 6,6262·10-34 J· s
с = 2,9979 ·108 M ·s-1
hc

 hc~
Electromagnetic spectrum
Absorption energy occurs at the excitation
elementary systems (nuclear, atomic, molecular)
and move her to a lower energic level to a higher
level.
a)
b)
c)
d)
e)
f)
g)
h)
Electromagnetic radiation is classified into
several types according to the frequency of its
wave; these types include (in order of increasing
frequency and decreasing wavelength):
radio waves,
microwaves,
terahertz radiation,
infrared radiation,
visible light,
ultraviolet radiation,
X-rays
gamma rays.
A spectrum is a condition that is not
limited to a specific set of values but can
vary infinitely within a continuum.
The electromagnetic spectrum is the range
of all possible frequencies of electromagnetic
radiation. The "electromagnetic spectrum" of
an object is the characteristic distribution of
electromagnetic radiation emitted or absorbed
by that particular object.
The spectrum of absorption
The intensity of the absorption varies as a
function of frequency, and this variation
is the absorption spectrum.
5
4 000
3 000
2 000
W ave num bers (c m-1 )
603,35
30
10
0
1 000
567,33
873,85
35
960,10
20
1416,31
470,50
403,92
471,50
873,80
1416,55
1456,08
50
567,13
15
1042,69
25
1456,58
45
603,56
1041,06
%Transmi ttance
5 5 em al 2 ve st
em al 2 oral
40
Types of spectrums:
1)
2)
3)
4)
5)
radiation (emission spectroscopy)
absorption (absoption spectroscopy)
reflection (spectroscopy of reflection)
dispersion (IR spectroscopy)
luminescence (luminescent spectroscopy)
3.Classification of spectroscopic methods of analysis.
1.
2.
3.
4.
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:
Electromagnetic spectroscopy involves interaction of
matter with electromagnetic radiation, such as light.
Electron spectroscopy involves interaction with electron
beams.
Dielectric spectroscopy involves the frequency of an
external electrical field.
Mechanical spectroscopy involves the frequency of an
external mechanical stress, e.g. a torsion applied to a piece
of material.
1.
2.
3.
II. Along with that distinction, they can be
classified on the nature of their interaction:
Absorption spectroscopy uses the range of the
electromagnetic spectra in which a substance
absorbs.
Emission spectroscopy uses the range of
electromagnetic spectra in which a substance
radiates (emits). The substance first must absorb
energy. This energy can be from a variety of
sources, which determines the name of the
subsequent emission, like luminescence.
Scattering spectroscopy measures the amount of
light that a substance scatters at certain
wavelengths, incident angles, and polarization
angles.
Method
Radiofrequency
(YAMR, EPR)
Microwave
Optical:
a) UPh
b) Visible
Infra-red (ICh,
CD)
X-ray
photography
Gamma-radiation
(kernel-physical)
Description of
energy‘s
quantum
101-10-1 m
10-1-10-3 m
10-200-400 nm
400-760 nm
760-106 nm
10-13000 сm-1
Process
Change of spins
kernels and electrons
Change of rotatory
states
Change states of
valency electrons
10-2-10 nm
Change swaying
states
Change of the state
of internal electrons
10-4-10-1 nm
Nuclear reactions
Rotational spectroscopy or microwave
spectroscopy studies the absorption and emission
of electromagnetic radiation (typically in the
microwave region of the electromagnetic spectrum)
by molecules associated with a corresponding
change in the rotational quantum number of the
molecule. The use of microwaves in spectroscopy
essentially became possible due to the development
of microwave technology for RADAR during
World War II. Rotational spectroscopy is only
really practical in the gas phase where the
rotational motion is quantized. In solids or liquids
the rotational motion is usually quenched due to
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 analysis
Spectrums used both for qualitative analysis and
also for quantitative analysis.
The qualitative analysis is the position (energy,
frequency, length of wave, wave‘s number) of
maximums (lines) in the electromagnetic
spectrum.
Quantitative analysis is an intensity
(amplitude) of spectral line is the function
of concentration substance. To use such
description of spectral line, which straight
proportional the concentration of a
substance.

For example, optical density:
A  lC


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
scattering of electromagnetic radiation by matter to
qualitatively or quantitatively study the matter or to study
physical processes.
Absorption: A transition from a lower level to a higher
level with transfer of energy from the radiation field to an
absorber, atom, molecule, or solid.
Emission: A transition from a higher level to a lower level
with transfer of energy from the emitter to the radiation
field. If no radiation is emitted, the transition from higher to
lower energy levels is called nonradiative decay.
Scattering: Redirection of light due to its interaction with
matter. Scattering might or might not occur with a transfer
of energy, i.e., the scattered radiation might or might not
have a slightly different wavelength compared to the light
incident on the sample.