Gas phase recombination of OH with NO and NO2

Abstract

The termolecular recombination of OH with NO and with NO₂ is studied for M=He, Ar, and N₂ at pressures from 1–10 torr and temperatures from 230–450°K in a flow tube using resonance fluorescence detection of OH radicals. The reactions are in their low pressure, third-order limit. The rate constants for the NO reaction at 295°K are 3.3, 3.4, and 5.8×10⁻³¹ cm⁶ sec⁻¹ in the above order of M gases. For the NO₂ reaction the corresponding values are 1.0, 1.0, and 2.3×10⁻³⁰, all with σ=±20% including estimates of systematic errors. Both recombinations show the expected negative temperature dependence, the Arrhenius activation energies being −1.7 kcal for NO and −1.8 kcal for NO₂. These results are compared with all other published data and with RRKM unimolecular calculations.