General information about spectroscopy. Helpful for GPAT preparation.

1. SPECTROSCOPY
Spectroscopy is the branch of science that probes molecular structures with the help of
electromagnetic radiation. It can also be employed for quantitative analysis.
Terminology-
a) Wavelength(lamda) : Distance between two successive crest(peak) and trough. Unit
of wavelength is metre (SI unit).
b) Frequency: It is the number of crest or trough that pass through a given point in one
second. Unit of frequency is cycle per second (cps) or Hertz or Fresnel.
c) Wave number: Reciprocal of wavelength is called wave number. It is the number of
wave per cm.
Expressed in Kaiser (K) or Kilo Kaiser (KK)
1 Kilo Kaiser = 1000K = 1000cm-1 .
Different types of energy associated with a molecule:
A) Translational Energy refers to the velocity of the molecule as a whole.
Et = mv2 / 2.
B) Rotational Energy is the energy associated with the rotation of the molecule.
Erot = Iw2 / 2.

2. C) Vibrational energy is the energy associated with the oscillation of atoms of the
molecule.
Evib = hv (v + ½).
Vibrational degrees of freedom for linear molecules such as water, methane is 3n – 6.
Vibrational degrees of freedom for non-linear molecules such as carbon dioxide is 3n –
5.
D) Electronic energy is the energy associated with the motion of the electron.
The total energy of a molecule is the sum of rotational energy, Vibrational energy and
Electronic energy.
Electronic energy > Vibrational energy > Rotational energy.
Photoelectric effect: Emission of electrons when light is incident on a metallic surface.
Plank’s equation:
E = h v Where E is the energy of photons in ergs.