Flash photolysis-resonance fluorescence kinetics study: Temperature dependence of the reactions OH + CO → CO2 + H and OH + CH4 → H2O + CH3

Abstract

Two reactions involving the transient chemical species OH(ν″ = 0) and the reactants CO and CH4 have been investigated over a temperature range of nearly 140°C. Of particular importance were the measurements made below 300°C where data has heretofore been lacking. The rate constant expressions in Arrhenius form are kCO = (2.15±0.19)×10−13 exp[−(160±80 cal mol−1)/R T] and kCH4 = (2.36±0.21)×10−12 exp[−(3400±175 cal mol−1)/R T]. Units are cm3 mol−1 · sec−1. Wide variations in the total pressure, H2O concentration, initial OH concentration, and the nature of the diluent gas showed no indication of complex secondary reactions. The activation energies reported in this work for both processes, virtually zero for Reaction (1) and 3400 cal mol−1 for Reaction (2), are incompatible with those same quantities previously reported at elevated temperatures and indicate either nonlinear Arrhenius behavior for these OH reactions or possibly errors in experimental measurements.