Abstract

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 (ρ_n), for perpendicularly polarized exciting light (ρ_s), and for parallel-polarized exciting light (ρ_p). The spectra investigated are those of CCl₄, CHCl₃, C₆H₆, and CS₂. The values obtained for ρ_n agree well with those obtained by numerous investigators. The values obtained for ρ_s and ρ_p seem to be in accord with the predictions of the theory. ρ_p seems to be highly sensitive to changes in symmetry of highly symmetrical vibrations, reaching a very large value for vibrations where ρ_n=.06 and rapidly approaches 1.00 for vibrations where ρ_n=.30 as well as for completely depolarized lines.

Measurements of ρ_n, ρ_s, and ρ_p 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.

© 1947 Optical Society of America

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