spectroscopy intro

1. Introduction to Spectroscopy
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2.  What is Spectroscopy?
 Measurement of the amount of radiations absorbed by a substance at various
wavelengths is called spectroscopy.
OR
 Spectroscopy is the study of interaction of electromagnetic radiations with
matter and measurement of absorption of radiations of various frequencies
upon interaction with the matter.
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3.  Wavelength, λ: Distance between two adjacent crests and troughs of the wave
in the beam of electromagnetic radiations.
 Units; angstrom, nanometer, micrometer and meter.
 Frequency, v: Number of waves passing a fixed point on the path of a beam of
radiation per unit time.
 Units; Hertz (Hz) or cycle per second.
 Wavenumber, ῡ: Number of waves per centimeter. Its unit is cm-1.
 Energy, E: Every photon of specific radiation possesses exactly the same
amount of energy which is, however different from the energy possessed by the
photon of different radiations. The unit of energy commonly used is Joule.
 Parameters to characterize Electromagnetic radiations:
 Electromagnetic Radiation:
 From of energy: commonly known as radiant energy.
 Ordinary light: more visible form of radiant energy.
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5. Electromagnetic Spectrum:
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7.  Relation between Energy, frequency, wavelength and
wavenumber.
E = hv = hc/λ = hcῡ
E = Energy
h = planks constant
v = frequency
c = velocity of radiations
λ = wavelength
ῡ = wavenumber
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8. Spectroscopic techniques
Techniques Underlying principle Information obtained
UV (200-400
nm)
VIS (400-800
nm)
Quantized absorption of UV/VIS
radiations leading to electronic
excitations.
Presence and nature of unsaturation,
particularly conjugation.
IR (2.5-16 µm or
4000-625 cm-1)
Quantized absorption of IR
radiations leading to vibrational
excitations.
Presence and environment of
functional groups, especially those
containing X-H type bonds such a C-
H, O-H and N-H or multiple bonds.
NMR
(60-6000 MHz)
Quantized absorption of radio
waves leading to transitions
between different spin orientations
of nuclei in the magnetic field.
Environment of magnetically active
nuclei, such as 1H, 13C etc., and
number of nuclei of each type.
MS (~70 eV ) Determination of mass-to-charge
ratio and relative abundance of the
ions formed on electronic
bombardment of molecules.
Molecular weight, molecular formula,
molecular structure and isotopic
abundance.
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10. Elemental Analyzer
Carbon Hydrogen & Nitrogen Analyzer can be used to
determine the carbon, hydrogen and nitrogen content in
coal, coke, food, soil, fertilizer, etcin the fields of power
plant, coal mine, metallurgy, steel factory and so on.

11. Mass spectrometry
Mass spectrometry (MS) is the study of ions created as a result of ionization/fragmentation as determined
electrically in the gas phase (neutral molecules are not observed)
Mass spectrometer

12. UV Spectrophotometer
 UV-visible spectrophotometer uses light over the ultraviolet range (185 - 400 nm) and visible range (400 -
700 nm) of electromagnetic radiation spectrum.

13. IR Spectrophotometer
 IR spectrophotometer: uses light over the infrared range (700 - 15000 nm) of electromagnetic radiation
spectrum.

14. NMR Spectroscopy
 Nuclear magnetic resonance (NMR) spectroscopy is the study of molecules by recording the interaction of
radiofrequency (Rf) electromagnetic radiations with the nuclei of molecules placed in a strong magnetic field.
NMR machine

15. 15  Instrumentation:
Detector
 Although different instruments are used for measuring absorbance in different
spectral regions, in their simplest form they all consist of five main
components: (1) source of electromagnetic radiations, (2) monochromator, (3)
sample cell, (4) a detector and (5) readout device.