Raman Spectroscopy:

You learnt about IR spectrometry in terms of its principle, instrumentation and applications. You would recall which the IR spectrum is a consequence of transitions amongst the quantised vibrational energy levels of the molecules on absorbing IR radiation.  Within this unit you would learn about Raman spectroscopy that also involves same energy levels but it differs on many other counts. The nature of radiation used, the mechanism of interaction between the radiation and matter, the necessary condition for the interaction, the selection rules, the sensitivity, required instrumentation and the resulting spectra are different in case of Raman spectroscopy. Further, even the information available from it is different; in fact it is complimentary to the one available from IR spectroscopy.

As in the previous unit, we shall begin by understanding the theory behind Raman spectroscopy in terms of the origin of the spectrum and its characteristic features. It will be followed by an account of the essential components of Raman spectrometers. Thereafter we shall take up the applications of Raman spectrometry in diverse areas. In the next block you will learn about spectrometric methods based on molecular fluorescence and molecular phosphorescence which are important spectroscopic method of analysis.

Objectives

After studying this unit, you should be able to:

• Describes Raman effect,
• Elaborates the origin of Rayleigh scattering,
• Define Raman effect in terms of classical wave theory and quantum theory of radiation,
• Describes Stokes and anti-Stokes lines and explain their origin,
• Contrast and compare Raman spectra with IR spectra,
• State a rule of mutual exclusion and elaborates its significance,
• Enlist the necessary components of the instrument needs for Raman spectroscopy,
• Define advantages of Raman spectroscopy, and
• Enumerate and elaborates several applications of Raman spectroscopy.