absorption spectroscopy

When a light passes through absorbing medium at right angle to the plane of surface or the medium or the solution, the rate of decrease in the intensity of the transmitted light decreases exponentially as the thickness of the medium increases arithmetically.

Accordingly, Lambert’s law can be stated as follows:

The entire range over which the electromagnetic radiation exists is known as electromagnetic spectrum. This electromagnetic spectrum ranges from very short wavelengths (including gamma and x-rays) to very long wavelengths (including microwaves and broadcast radio waves). The following chart displays many of the important regions of this spectrum.

INSTRUMENTATION

Instruments for measuring the absorption of U.V. or visible radiation are made up of the following components;
1. Sources (UV and visible)
2. filter or monochromator
3. Sample containers or sample cells
4. Detector

1. Radiation source
It is important that the power of the radiation source does not change abruptly over its wavelength range.

Solvent Effect
Solvents play an important role in UV spectra. Compound peak could be obscured by the solvent peak. So a most suitable solvent is one that does not itself get absorbed in the region under investigation. A solvent should be transparent in a particular region. A dilute solution of sample is always prepared for analysis. Most commonly used solvents are as follows.

It was earlier stated that σ, π, and n electrons are present in molecule and can be excited from the ground state to excited state by the absorption of UV radiation. The various transitions are n→∏*, ∏→∏*, n→σ*, & σ →σ*

The word spectroscopy is derived from spectrum which means a bend of different colours formed due to difference in wavelength and skopin means examination or evaluation.

Thus, spectroscopy is the branch of science that deals with the examination or evaluation of spectrum.