The vibrational Stark effect on the doubly degenerate nu(19) modes of the benzene guest molecules in Hofmann type clathrates

An alternative mechanism is proposed for the observed splitting of the nu ( 19) gamma (CH) mode of the benzene guest molecules in Hofmann type clathrat es to the one presented previously.(1) According to the proposed model, the splitting is due to the vibrational Stark effect. A simple quantum theoret ical model for this effect is derived, based on the degenerate-case station ary perturbation theory, both with and without explicit inclusion of the vi brational angular momentum. The model allows estimation of the relative fie ld strengths at the enclathration sites of the guest molecules in a series of structurally similar clathrates. The derived equations may be used for c alculation of the local field strength as well, if particular anharmonic co upling constants for enclathrated species are available. The predictions of the proposed method are fully in line with the observed room temperature-l ow temperature trends for a particular clathrate, as well as with the trend s in the series of isostructural clathrate compounds for which experimental data are available.