A method is described for obtaining the true relative intensities of lines in a Raman spectrum excited by natural unpolarized light. Detection and intensity measurement was accomplished by means of a large photoelectric grating spectrograph. Correction of intensity measurements for the variable polarization and line breadth of the Raman lines is accomplished by methods described in this paper. Depolarization factors have been measured for natural unpolarized exciting light (ρn), for perpendicularly polarized exciting light (ρs), and for parallel-polarized exciting light (ρp). The spectra investigated are those of CCl4, CHCl3, C6H6, and CS2. The values obtained for ρn agree well with those obtained by numerous investigators. The values obtained for ρs and ρp seem to be in accord with the predictions of the theory. ρp seems to be highly sensitive to changes in symmetry of highly symmetrical vibrations, reaching a very large value for vibrations where ρn = .06 and rapidly approaches 1.00 for vibrations where ρn = .30 as well as for completely depolarized lines.
Measurements of ρn, ρs, and ρp were made for the Rayleigh scattering of these same molecules, using the identical apparatus employed for the Raman spectrum. Qualitatively the measurements are satisfactory. The presence of parasitic light shows that modifications will have to be made in the scattering apparatus to obtain satisfactory quantitative ρ values, especially for highly isotropic molecules.PDF Article