Raman spectra of solid benzene under high pressures

Abstract

Raman spectra of benzene I and benzene II have been obtained to pressures of 40 kbar at 77 and 295 K. Eight lattice mode frequencies were observed for benzene I, including one feature of the spectrum that has not been previously reported. At 45 kbar and 77 K, lattice mode frequencies of benzene I are about twice their atmospheric pressure values. The spectra of some internal modes as functions of pressure are reported. The lattice dynamics of the benzene crystals were studied by calculations using atom-atom potentials to predict the wavenumbers and normal coordinates of the lattice modes. A simple change-of-polarizability argument was used together with structural direction cosines and calculated normal coordinates to estimate the relative intensities expected for the Raman spectra. The results of the intensity and dynamical calculations were combined to make a complete assignment of the lattice mode Raman spectra of both phases of benzene.