LASER BEAT FREQUENCY SPECTROSCOPY

We have seen that the spectral distribution of light scattered from spherical molecules and from rod-shaped molecules may be analyzed in terms of the translational and rotational diffusion coefficients of these molecules. These coefficients may, in turn, be related to the size and conformation of the molecules. In addition, laser beat frequency spectroscopy can be used to analyze the spectrum of light scattered from pure liquids near their critical points and solutions near their critical mixing points. These phenomena are fully discussed by Alpert, Yeh, and Cummins (20), Ford and Benedek (10), Lastovka and Benedek (11), Mountain (21), Chu (22), and in the book by Fabelinskii (23). A theoretical calculation of the spectral distribution expected of the light scattered from fluctuations about equilibrium in a chemically reactive solution has been made by Blum and Salsburg (24). Laser spectroscopy may, therefore, find application in the measurement of the relaxation rates of fast reactions. In our laboratory we are using laser self-beat spectroscopy to investigate the conformational changes that occur in biomolecules under the influence of environmental changes such as changes in pH, temperature, and dielectric constant of the solvent.