Quenching of OH (A 2Σ+, v′=0) by several collision partners between 200 and 344 K. Cross-section measurements and model comparisons

Abstract

The cross-sections for the collisional quenching of OH(A ²Σ⁺, v′=0) by CO, CH₄, H₂ and Kr were determined between 200 and 344 K in a flash-photolysis system. In all cases cross-sections increased with decreasing temperature, consistent with attractive forces dominating the collision process. For CO, the cross-section increased from 30.0±2.3 Ų at 344±1 K to 50.3±3.8 Ų at 200±1 K. The corresponding values for the other collision partners are: 25.3±1.9 to 37.4±2.8 Ų (CH₄); 8.0±0.6 to 11.8±0.9 Ų (H₂) and 7.3±0.5 to 11.6±0.8 Ų (Kr). Cross-sections were also determined at 344 K for N₂, O₂, CO₂ and H₂O collision partners, for which values had previously been measured in the range 204–294 K. For all collision partners, an empirical formula was used to describe the data over the range 200–2300 K in order to enable quenching corrections to be made during the detection of OH by laser-induced fluorescence in a variety of media. The temperature-dependent cross-sections were analysed using a Parmenter–Seaver well-depth correlation, and are compared with the predictions of a model based on the ‘harpooned ’ mechanism, together with a realistic interaction potential.