Motions of Molecules in Condensed Systems. IX. Infrared Absorption Anisotropy and Induced Molecular Motion in a Single Crystal of Benzene

Abstract

Infrared absorption spectra were observed with radiation polarized linearly along each of the two extinction axes contained in a thin cross section from a single crystal of benzene grown especially for this purpose. The spectra indicate consistently that the cross section was the 010 plane, that they record separately the absorptions polarized along the a-axis and the c-axis, respectively. The anisotropies of the induced absorptions exhibited by five fundamental molecular vibrations (ones that appear only in spectra for condensed phases) are all quite similar and may even be identical. It thus appears that the induced motions, super-imposed upon the several intrinsic ones by the perturbing intermolecular interactions, have a property of similarity independent of the differing natures of the intrinsic motions that are being perturbed.