Matrix–molecule interactions, dynamics, and exchange phenomena in low temperature matrices: SF6 in argon and krypton

Abstract

High resolution infrared studies of argon/SF6 and krypton/SF6 matrices at 10 000/1 show an unexpected amount of structure; 10–12 peaks are observed in argon and six or more peaks in krypton matrices for the n3 mode. Studies in which the deposition temperatures are varied, in conjunction with the structure observed for combination modes and temperature reversible spectral changes, allowed differentiation between multiple trapping sites and site symmetry splittings. We conclude that there are at least six different sites for monomeric SF6 in argon and at least three sites in krypton. Two sites in argon and two in krypton exhibit site symmetry splittings. Temperature dependence studies have shown striking spectral changes wherin for three of these sites (one in argon and two in krypton) the peaks, due to site symmetry splitting, coalesce as the temperature is raised. The temperature dependence can be explained in terms of exchange dephasing involving two high energy fundamentals and a local phonon mode. The dynamics associated with motional collapse of the high enery fundamentals corresponds to rapid site-to-site exchange on a less than nanosecond time scale resulting in higher effective site symmetry as observed by infrared. Unusual 32S–34S isotope effects have also been observed for the spectra of these low temperature matrices.