VIBRATIONAL RELAXATION CORRELATION FUNCTIONS AS A PROBE OF INTERMOLECULAR FORCES IN CRYSTAL, LIQUID CRYSTAL, ISOTROPIC LIQUID, AND SOLUTION PHASES

Abstract

Correlation functions obtained from scattering associated with the Raman CN stretching mode of 4 cyano 4^{\prime}octyloxybiphenyl (8OCB) have been obtained in crystal, aligned nematic and smectic phases, as well as in isotropic liquid and solutions $(CC\ell_{4},$, benzene, $CHC\ell_{3}$, and $CH_{3}SCN$ solvents). The functions are purely vibrational relaxation to 4 psec. These represent first such Raman correlation functions from a liquid crystal, and the first vibrational correlation functions from a large, non-rigid molecule. The results are analyzed in the framework of the dephasing theory. They yield new evidence on each of several possible mechanisms, both in the slow and fast modulation regimes. Of particular interest is the fact that the different solvents affect the CN stretching mode vary differently. This is in turn different from the effect of these same solvents on benzonitrile and acetonitrile. These results can be further quantified by subdividing into the 0-0.7, 0.7-1.5, and 1.5-4 psec ranges. The results shed considerable light on the intermolecular interactions between 80 CB and related molecules.