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

Rate coefficients are reported for the removal of H2O in selected vibration al states in collisions with H atoms. Pulses of tunable infrared radiation have been employed to excite H2O molecules to the specific vibrational leve ls \04 >(-), \13 >(-), \03 >(-), \12 >(-) and \02 >(-)2 >, where the notati on is that used by Sinha et al. (A. Sinha, M. C. Hsaio and F. F. Crim, J.Ch em. 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 o f 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. Rat e coefficients are reported for three kinds of process: (i) the removal of excited H2O molecules from the initially excited level by the sum of reacti on and relaxation with H atoms, (ii) the relaxation of excited H2O molecule s from the initially excited level by collisions with unexcited H2O, and (i ii) the relaxation of OH(v=1) by H atoms and H2O. The results are compared with previous experimental data, especially that on selective vibrational e nhancement of endothermic chemical reactions, and with the results of theor etical calculations on the H+H2O reaction.