The Electromagnetic Spectrum (EM) is consist of radiation of a wide range of wavelengths (λ). According to the Quantum Mechanics, all these radiations have a dual and seemingly contradictory nature. EM radiations have the properties of both wave and particle. So that these radiations can be described in the terms of its wavelength (λ) or its frequency (ν). It can also be described as if it consisted of particles called quanta or photons. Photons are known as quantized energy.
The EM radiation travel through a vacuum at the same velocity(c), called the velocity of light; which is 2.99792458 Χ 108 ms-1. The frequency of a wave is usually given by Hertz (Hz). The energy of a EM radiation is directly proportional to its frequency,
E = hν
where,
h = Planck's constant, 6.63 x 10-34 J s
ν = the frequency (Hz)
E = energy
This means that the higher the frequency of radiation the greater is its energy.
Since, ν = c/λ, the energy of a EM radiation inversely proportional to its wavelength.
E = hc/λ
where, c = velocity
When the energy of these EM radiations are bombarded with the organic molecules, the energy is absorbed by the molecules and they shows transitions in their energy levels. The molecules are in continuous motion and these motions can be resolved into different component as below,
- Rotational energy :- this is the energy due to the rotation of the molecule resolving about an axis of its gravity.
- Vibrational energy :- This is the energy due to the vibration of the molecule.
- Electronic energy :- This is the energy that possessed by the electron from its definite energy levels.
- Nuclear spin energy :- This the energy due to the spin of the nuclei of the molecule.
There are various energy levels in the molecules according to their energy type, they are; Rotational energy level, Vibrational energy level, Electronic energy level, and the Nuclear energy level.
Eelectronic > Evibrational > Erotational > Enuclear spin ; this means that the EM radiation with higher energy can effect the electronic transitions and the EM radiation with lower energy can effect the nuclear spin transitions. This can be illustrated by following table as well,
| Radiation type | Wavelength/cm | Energy | Transition effect |
|---|---|---|---|
Radio
|
104 - 106
|
10-10 - 10-8
|
Nuclear spin
|
TV
|
102
|
10-6
|
Nuclear spin
|
Radar
|
1
|
10-4
|
Nuclear spin
|
Microwaves
|
10-1
|
10-3
|
Rotational
|
far IR
|
10-2
|
10-2
|
Vibrational
|
near IR
|
10-4
|
1.24
|
Vibrational
|
Visible
|
10-5
|
1.55 - 3
|
Electronic
|
UV
|
10-6
|
4
|
Electronic
|
X-ray
|
10-8
|
104
|
Electronic
|
γ- ray
|
10-10
|
106
|
Nuclear
|
Cosmic ray
|
10-12
|
108
|
Nuclear
|
No comments:
Post a Comment