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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. [ABSTRACT FROM AUTHOR]

Vibrational energy transfer from SF6 to N2O was studied by using a pulsed CO2 laser for multiphoton excitation of SF6 and monitoring the 4.5 μm emission from N2O(v3=1). The initial average energy of SF6 was selected by varying the fluence of the laser. The vibrational temperature of the ν2 mode of N2O was determined by measuring the attenuation of the fluorescence with a cold gas filter. The vibrational temperature of the ν3 mode was estimated by equating the SF6 and N2O(ν3) vibrational temperatures at the fluorescence maximum. The principal finding of this study is that N2O(ν2) is preferentially excited. While the mode specificity of the VV transfer declines with energy, it is greater than expected statistically. We also observed that the relaxation of ν2 is an order of magnitude slower than the relaxation of ν3. A kinetic model which accounts for most of the observations shows that VV transfer from SF6 to N2O occurs from high lying states of SF6 while the decay of N2O occurs by back transfer to the discrete levels of SF6. The slow relaxation of the bending mode of N2O indicates the existence of a bottleneck in VV transfer between N2O(ν2) and the discrete levels of SF6, which may be caused by a mechanism involving long-range attractive forces. [ABSTRACT FROM AUTHOR]

The relaxation rate constants for DCl(v=1) in liquid xenon at 211 K and HCl(v=1) in liquid krypton at 190 K are reported. Both the DCl–DCl and HCl–HCl rate constants are similar to the corresponding gas phase rate constants at the same temperature, and the relaxation appears amenable to an isolated binary collision (IBC) description. As in the gas phase, the rate constant for DCl–DCl deactivation in liquid xenon is found to be smaller than that for HCl–HCl relaxation in liquid xenon, despite the smaller energy defect for the DCl relaxation process. This suggests that rotational degrees of freedom are also involved in the liquid phase vibrational relaxation of these molecules. The observed relaxation rates for DCl(v=1) by liquid xenon and HCl(v=1) by liquid krypton are found to be within an order of magnitude of values estimated from various forms of the IBC model. More careful comparisons await values of the appropriate gas phase relaxation rate constants near 200 K. Finally, certain features of the mechanism for production of vibrationally excited HCl and DCl are considered. [ABSTRACT FROM AUTHOR]

The deactivation of vibrationally excited HCl produced via excimer laser photolysis of chloroethylenes has been studied in both the gas phase and in liquid xenon solution. The rate of deactivation of HCl* by the chlorethylene parent is significantly faster in liquid xenon than in the gas phase. This occurs due to enhancement of the vibration–vibration energy transfer probability in solution. The nature of this enhancement is discussed. [ABSTRACT FROM AUTHOR]