Pressure Effect on the Inter- and Intramolecular Vibrations of Hexachlorobenzene Crystal

Abstract

The effect of pressure on the Raman active inter- and intramolecular vibrations of the hexachlorobenzene crystal was studied under hydrostatic pressure up to 5.5 GPa. The Raman frequencies of the inter- and intramolecular vibrations increased monotonically and some bands due to the degenerate intramolecular vibrations were resolved into doublets with increasing pressure. The pressure-induced frequency shift and factor group splitting of the bands due to the intramolecular vibrations were calculated using an intermolecular potential of the atom–atom type. These results show that (1) no phase transition takes place in the crystal under pressure up to 5.5 GPa, (2) the observed pressure-induced frequency shift is mainly caused by the repulsive force between chlorine atoms belonging to the adjacent molecules, and (3) the observed splitting of the bands due to the degenerate intramolecular vibrations is caused by the different intermolecular force acting to the a and b vibrational modes.

Probing Structural Perturbation in a Bent Molecular Crystal with Synchrotron Infrared Microspectroscopy and Periodic Density Functional Theory Calculations

“…For numerical integration in DFT, the pruned grid of 75 radial and 974 angular points (75,974) was used. The suitability of the computational approach was confirmed by comparison of the spectra calculated by periodic DFT with literature data on experimental spectra recorded from an HCB single crystal. − The periodic DFT computations reproduce remarkably well the experimental single-crystal data (for discussion on the spectral comparison, see the Supporting Information and Table S1 therein). The computational method proved to be robust, and reflects faithfully the non-equilibrium conditions in a strained crystal.…”

“…The fitted bands are shown in Figure , and their assignments are presented in Table . The bands in the spectrum of the straight crystal (Figure c,f) were assigned based on computational analysis (Table S1, Supporting Information) and comparison with earlier assignments. − …”

“… a Scaled DFT frequencies (the unscaled values are in parentheses). b Fitted to the experimentally recorded spectrum (Figure ). For a complete list of vibrational modes and frequencies see Table S1, Supporting Information. c References − . d Approximate band description and symmetry. …”