The Hyper Raman Effect
My first research problem in Raman spectroscopy was concerned with the measurement of vibrational Raman intensities. This involved a detailed analysis, based on the Placzek polarizability theory,1 of the factors controlling Raman intensities. This revealed the considerable experimental problems which arise in making meaningful intensity measurements when the scattering sample is illuminated with an extensive non-directional light source like a mercury arc. With laser excitation of Raman spectra, these problems are much simplified because of the unique directional properties of laser radiation. This is but one of the many advantages that lasers possess as sources for Raman spectroscopy. Many of the other advantages are dealt with specifically in subsequent chapters : these include the study of rotational and vibration-rotation Raman spectra under high resolution (Chapter 6), the Raman spectra of crystals (Chapters 5 and 8), and the investigation of vibrational Raman spectra in the vapour phase (Chapter 5). The general ease with which good quality Raman spectra can be obtained from very small quantities of imperfect samples using laser excitation will also be apparent from the relative abundance of information now available from Raman spectroscopy and discussed in the several chapters dealing with vibrational assignments (particularly Chapters 3, 13, 16 and 17).
KeywordsResonance Condition Scattered Radiation Spectral Element Transition Moment Raman Effect
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