The reaction of hydrogen atoms with ozone as a source of vibrationally excited OH(X 2πi)v = 9 for kinetic studies

Abstract

The reaction of measured initial concentrations of hydrogen atoms with ozone was used to produce vibrationally excited OH(X ²π_i)_v?9 in a fast flow discharge system at 1.1±0.1 Torr total pressure in argon at 300±3 °K. The kinetic behavior of the highest vibrational level of OH produced (v = 9) [designated OH(9)] was characterized by a variety of experiments including (1) determination of both its rates of formation and decay under conditions of excess H, as well as excess O₃, (2) examination of the effects of added quencher/reactants, and (3) determination of the absolute concentrations of OH(9) using published Einstein A factors. In addition, the change in these concentrations of OH(9) for a given set of initial conditions was examined when the total pressure, nature of the carrier gas, coating of the flow tube walls, and concentration of initial, excess hydrogen atoms were varied. The results of these studies indicate that OH(9) is removed sufficiently rapidly from the system that pseudo‐first‐order kinetics cannot be applied to obtain absolute rate constants for its reactions and energy transfer processes. However, relative rate constants can be obtained and are reported for CO₂, Ar, and N₂ relative to O₂. These data are interpreted in light of the two published sets of values for the Einstein A factors, which differ by more than an order of magnitude. The need for accurate values of these A factors in order to convert our relative rate constants into absolute values, as well as to use in understanding the chemistry of the upper atmosphere, is discussed. The rotational temperature of OH is shown to be 308±18 °K in both excess H and excess O₃.