Intramolecular vibrational relaxation of a polyatomic in the solid state. I. DCN in Xe

Vibrational relaxation of DCN isolated in Xe matrices has been studied by laser-excited vibrational fluorescence. The C–D stretch ν3 was excited and fluorescence was observed from overtones and combinations of the ν1 and ν2 modes. The decay rates of the vibrational levels range over several orders of magnitude from 3×108 s−1 for ν3 to 2.1×105 s−1 for ν2. A kinetic model for the relaxation was solved to give a complete set of rate constants for the vibrational transitions. The rates, together with the relative fluorescence intensities, show that there is a dominant relaxation channel. The relative importance of competing channels depends on changes in energy and in vibrational quantum number of the transfers. Within the ν2 manifold, the rate constants for Δv2=1 transitions follow kν,ν−1=vnk1,0 with n<1.3. The rate constants increase only modestly with temperature indicating that the excess vibrational energy is transferred to guest modes such as rotation or translation rather than to bulk phonons.