Quenching of OH (A 2Σ+, v′=0) by H2, N2O, and hydrocarbons at elevated temperatures

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Abstract
Rate constants for collisional quenching of OH (A 2Σ+, v’=0) have been measured for H2, N2O, and ten hydrocarbon molecules at temperatures near 1200 K. A laser pyrolysis/laser fluorescence technique was used, in which a pulsed CO2 laser heats a gas mixture and a pulsed ultraviolet laser excites the OH. The rate constants are obtained from the pressure dependence of the direct time decay of the fluorescence. The resulting thermally and rotationally averaged cross sections are lower than those at room temperature, where comparisons are available; this is in accord with a picture of quenching involving attractive interactions between OH and the quencher. The bigger hydrocarbons such as butane and especially butenes have particularly large cross sections, which a simple attractive forces theory cannot explain.