Relaxation of H2O from its /04>- vibrational state in collisions with H2O, Ar, H2, N2, and O2.

Abstract

We report rate coefficients at 293 K for the collisional relaxation of H2O molecules from the highly excited /04>(+/-) vibrational states in collisions with H2O, Ar, H2, N2, and O2. In our experiments, the mid R:04(-) state is populated by direct absorption of radiation from a pulsed dye laser tuned to approximately 719 nm. Evolution of the population in the (/04>(+/-)) levels is observed using the combination of a frequency-quadrupled Nd:YAG laser, which selectively photolyses H2O(/04>(+/-)), and a frequency-doubled dye laser, which observes the OH(v=0) produced by photodissociation via laser-induced fluorescence. The delay between the pulse from the pump laser and those from the photolysis and probe lasers was systematically varied to generate kinetic decays. The rate coefficients for relaxation of H2O(/04>(+/-)) obtained from these experiments, in units of cm3 molecule(-1) s(-1), are: k(H2O)=(4.1+/-1.2) x 10(-10), k(Ar)=(4.9+/-1.1) x 10(-12), k(H2)=(6.8+/-1.1) x 10(-12), k(N2)=(7.7+/-1.5) x 10(-12), k(O2)=(6.7+/-1.4) x 10(-12). The implications of these results for our previous reports of rate constants for the removal of H2O molecules in selected vibrational states by collisions with H atoms (P. W. Barnes et al., Faraday Discuss. Chem. Soc. 113, 167 (1999) and P. W. Barnes et al., J. Chem. Phys. 115, 4586 (2001).) are fully discussed.