Rate coefficients for the reaction and relaxation of H2O in specific vibrational states with H atoms and H2O

Abstract

Rate coefficients are reported for the removal of H₂O in selected vibrational states in collisions with H atoms. Pulses of tunable infrared radiation have been employed to excite H₂O molecules to the specific vibrational levels ∣04〉^-, ∣13〉^-, ∣03〉^-, ∣12〉^- and ∣02〉^-2〉, where the notation is that used by Sinha etal. (A. Sinha, M. C. Hsaio and F. F. Crim, J.Chem. Phys., 1991, 94, 4928), in the presence of known concentrations of both H atoms and H₂O. OH radicals formed either in v=0 or v=1 by the reaction of H atoms with the vibrationally excited H₂O are observed by laser-induced fluorescence. Kinetic data are derived from the variation of LIF intensity with delay time between the infrared pump and ultraviolet probe lasers. Rate coefficients are reported for three kinds of process: (i) the removal of excited H₂O molecules from the initially excited level by the sum of reaction and relaxation with H atoms, (ii) the relaxation of excited H₂O molecules from the initially excited level by collisions with unexcited H₂O, and (iii) the relaxation of OH(v=1) by H atoms and H₂O. The results are compared with previous experimental data, especially that on selective vibrational enhancement of endothermic chemical reactions, and with the results of theoretical calculations on the H+H₂O reaction.