ABSTRACT
When monochromatic light strikes a sample, almost all the observed light is scattered elastically (Rayleigh scattering) with no change in energy (or frequency). A very small portion of the scattered light, ~1 in 1010, is inelastically scattered (Raman scattering) with a corresponding change in frequency. The difference between the incident and scattered frequencies corresponds to an excitation of the molecular system, most often excitation of vibrational modes. By measuring the intensity of the scattered photons as a function of the frequency difference, a Raman spectrum is obtained. Different from fluorescence spectrum and reflectance spectrum, Raman peaks are typically narrow and in many cases can be attributed to the vibration of specific chemical bonds (or normal mode dominated by the vibration of a functional group) in a molecule. As such, it is a “fingerprint” for the presence of various molecular species and can be used for both qualitative identification and quantitative determination (Grasselli and Bulkin 1991).
