V–V energy transfer in the HCl–CO system: A comparison between measurements in the gas phase and in liquid xenon solution

Abstract

Both UV photolysis and overtone excitation(followed by energy relaxation) are used to produce vibrationally excited HCl in HCl–CO–liquid xenon (LXe) solutions. Rate constants for V–V transfer from HCl (v=1) to CO are reported both for the gas phase (210–295 K) and for liquid xenon solutions (210 and 229 K). In the gas phase, the probability of V–V transfer is found to increase with temperature (by approximately 50%) over the measured range. Liquid phase rate constants are approximately twice as fast as gas phase rate constants at the same temperature. The experimental ratio of liquid to gas phase rate constants is close to that predicted by a simple isolated binary collision (IBC) model employing hard sphere pair distribution functions. Such a model is clearly oversimplified for the present system, and both its inadequacies and possible reasons for its ability to reproduce the experimentally measured ratios are discussed. Despite evidence of H and/or Cl atom chemistry in solution, the technique of UV (193 nm) photolysis of HCl–CO–liquid xenon solutions, which produces vibrationally excited HCl, is also found to yield an accurate value of the HCl (v=1) →CO V–V rate constant. Possible reaction products and uses of this technique to generate mobile radical species in rare gas solution are considered.