Vibrational relaxation of H2O by H2, HCl, and H2O at 295 K

Abstract

A laser induced fluorescence method has been used to measure rate constants for vibrational relaxation of the equilibrated ν1 and ν3 stretching level reservoir, the 2ν2 bending overtone level, and the ν2 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)×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)×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 2ν2 level and the 2ν2 level was relaxed predominantly to ν2. Following direct laser excitation, the rate constant for relaxation of the equilibrated ν1+ν2 and ν3+ν2 combination vibrational levels of H2O by H2O was measured to be (1.6±0.2)×10−10 cm3 molecule−1 s−1. Direct relaxation to the ν1 and ν3 fundamental levels was experimentally determined to account for <40% of the relaxation rate constant.

A full nine-dimensional potential-energy surface for hydrogen molecule-water collisions

“…Figure 1 compares our results with the current best estimate which is based on an empirical equation derived from shock-tube measurements of diatomic systems [39,40]. The single experimental result of Zittel and Masturzo [41] at 295 K is also shown. For temperatures above 1500 K, our results are about one order of magnitude greater than the empirical predictions.…”

Collisional excitation of water in warm astrophysical media

“…This finding was observed in many other hydrogen systems as demonstrated by strongly nonlinear Landau-Teller plots (see for example the theoretical work of Dashevskaya et al (2007) for H 2 +H 2 ). Furthermore, even negative temperature dependence was observed experimentally close to room temperature for the self-relaxation of H 2 O (Zittel & Masturzo 1991). It is therefore possible that the rate for vibrational relaxation of H 2 O by H 2 increases below 300 K.…”

“…In the present study, the above procedure was applied to all para and ortho-H 2 O levels above the lowest 14 and below a threshold energy of 5000 cm (Zittel & Masturzo 1991), as illustrated in Fig. 4.…”

“…For higher vibrational modes of water, the only available data is provided by the measurements of Zittel & Masturzo (1991) at 295 K. In addition to the (010) bending level, these authors measured rate coefficients for vibrational relaxation of the (100) and (001) stretching level reservoir and the (020) bending overtone. Since the relaxation between the nearly resonant (100) and (001) stretching levels is far more rapid than relaxation from the stretching levels, (100) and (001) were experimentally found to reach equilibrium immediately and to relax as a single reservoir.…”

Overtone vibrational spectroscopy in H2-H2O complexes: A combined high level theoretical ab initio, dynamical and experimental study

“…Beyond issues of van der Waals dimer formation, however, there is also substantial fundamental interest simply in inelastic scattering between H 2 and H 2 O species, 34 for which the precise intermolecular potential energy surface plays a role of central importance. For example, the lowest rotational spacings in the para H 2 (358 cm −1 ) and ortho H 2 (600 cm −1 ) nuclear spin manifolds are greatly in excess 35 of those of both para H 2 O (37.1 cm −1 ) and ortho H 2 O (18.6 cm −1 ), where the para/ortho (or p/o) designation refers to I = 0 vs I = 1 coupling of the H atom nuclear spins.…”