RATE CONSTANT FOR THE REACTION H + NO2 FROM 195-K TO 400-K WITH FP-RF AND DF-RF TECHNIQUES

Absolute rate constants for the reaction of atomic hydrogen with nitrogen dioxide have been measured over the temperature range 195-400 K with two independent techniques both of which utilize resonance fluorescence detection of H. The reaction was studied from 230 to 400 K with the flash photolysis-resonance fluorescence (FP-RF) technique. No variation with temperature was observed, the best representation for the rate constant being (1.32 ± 0.12) × 10-10 cm3 molecule-1 s-1. The discharge flow-resonance fluorescence (DF-RF) technique was also used to study the reaction over the temperature range 195-368 K. The results are best represented by the temperature-independent value of (1.50 ± 0.26) × 10-10 cm3 molecule-1 s-1. The mean value of the two determinations for 195 ≤ T ≤ 400 K is then k1 = (1.41 ± 0.26) × 10-10 cm3 molecule-1 s-1 where the error is two standard deviations. The combined result is compared with previous results, both direct and indirect. The reaction is also considered theoretically, especially with regard to the question of the temperature dependence and the absolute magnitude of the rate constant.