Intramolecular vibrational relaxation of a polyatomic in the solid state. II. HC14N and HC15N in Ar, Kr, and Xe

Publisher Website
Google Scholar
Abstract
The vibrational relaxation of HC14N and HC15N isolated in Ar, Kr, and Xe matrices was studied by laser‐excited vibrational fluorescence. Complete sets of rate constants for the unimolecular relaxation of ν3 excitation through the ν1 and ν2 manifolds were obtained for HCN/Xe. At low temperatures the (1,00,0) level is a metastable trap and at increased temperatures detrapping shifts the relaxation route from the ν1 to the ν2 manifold. Dipole–dipole hopping of ν3 and ν2 quanta was observed and treated quantitatively with Förster theory. The temperature dependence of rates indicates that the vibrational energy is transferred to a local guest mode. The increase in rate, kXe<kKr<kAr, with steepness of repulsive potential and with vibrational frequency in the matrix shows that relaxation is caused by a repulsive interaction between guest and matrix. Gas phase theory is adapted to model hard ‘‘collisions’’ with the matrix cage; it indicates that translation rather than rotation is the accepting mode. The success of this model in treating the dependence of rate on vibrational energy and quantum number change suggests that it will be useful for predicting relaxation mechanisms and rates in other systems.