VIBRATIONAL-RELAXATION OF H2O BY H2, HCL, AND H2O AT 295-K

A laser induced fluorescence method has been used to measure rate constants for vibrational relaxation of the equilibrated nu-1 and nu-3 stretching level reservoir, the 2-nu-2 bending overtone level, and the nu-2 bending level of H2O by H2 and HCl at 295 K. The rate constants for relaxation by H2 were found to be (8.0 +/- 1.1), (29 +/- 4), and (13 +/- 2) x 10(-13) cm3 molecule-1 s-1, respectively. For relaxation by HCl the rate constants were (8.4 +/- 1.2), (47 +/- 7), and (24 +/- 4) x 10(-12) cm3 molecule-1 s-1, respectively. Relaxation by intermolecular V --> V transfer was experimentally determined to account for < 8% of the rate constant for relaxation of the H2O stretching levels by HCl and was estimated to contribute < 16% of the rate constant for relaxation of the bending overtone level. For both collision partners, the H2O stretching levels were relaxed predominantly to the 2-nu-2 level and the 2-nu-2 level was relaxed predominantly to nu-2. Following direct laser excitation, the rate constant for relaxation of the equilibrated nu-1 + nu-2 and nu-3 + nu-2 combination vibrational levels of H2O by H2O was measured to be (1.6 +/- 0.2) x 10(-10) cm3 molecule-1 s-1. Direct relaxation to the nu-1 and nu-3 fundamental levels was experimentally determined to account for < 40% of the relaxation rate constant.