Investigation of OH-H2 and OH-CO reactions using argon-sensitized pulse radiolysis

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Abstract
Gas‐phase OH radical reactions with H2 and CO were studied using pulse radiolysis absorption spectroscopy in Ar‐H2O‐H2 and Ar‐H2O‐CO systems. Computer simulation was used to examine the contribution of various reactions involved in OH decay and to confirm the experimentally measured bimolecular rate constants of OH+H2 and OH+CO reactions. In the hydrogen‐argon‐water system, it was found that the OH+H reaction makes a substantial contribution to OH decay in competition with the process OH+H2. The value of the OH+H2 abstraction rate constant, (3.2±0.7)×10−15 cm3 molecules−1 s−1, obtained empirically from a plot of the pseudo‐first‐order rate constant for OH consumption versus H2 pressure was about 50% lower than most literature values, but proved to be acceptable in the dynamic simulations. Although some 30 reactions are needed to describe the Ar‐H2O‐CO system, the OH concentration decreases almost exponentially, mostly by the OH+CO addition reaction, with small contributions by other processes. The empirically determined OH+CO bimolecular rate constant of (1.55±0.13)×10−13 cm3 molecule−1 s−1 agreed well with literature values determined in the presence of Ar buffer gas and also led to consistent predictions in the computer simulation work.