Dynamics of intramolecular vibrational redistribution in propargylchloride molecule studied by time-resolved Raman spectroscopy

We have studied the dynamics of intramolecular vibrational energy redistribution (IVR) from the initially excited mode ν1 (acetylene-type H–C bond) in H–CC–CH2Cl molecules in the gaseous phase by means of anti-Stokes spontaneous Raman scattering. The energy relaxation from ν1 due to IVR was estimated to occur on the time-scale τ ≈ 750 ps, which is one of the slowest IVR time-scales reported so far. The deactivation due to molecular collisions occurred with a rate constant of ≈8.5 μs−1 Torr−1, and was slower than the IVR process. A theoretical model which is based on the idea of statistical nature of couplings and incompleteness of IVR (expressed in the form of the so-called dilution factor) is proposed. The model provides rationalization for the observed kinetics and suggests that the IVR process is mediated by not only anharmonic but also vibrational–rotational interactions.