Rate measurements of reactions of OH by resonance absorption. Part 1.—Reactions of OH with NO2and NO

Abstract

Some reactions of the OH radical, which can be initiated by flash photolysis, have been studied using resonance absorption to follow how the OH concentration varies with time. The reaction OH + NO2(+M)→ HNO3+ M (4), has been investigated at 300 K and 416 K, and at total pressures (of He) between 20 and 300 Torr. In this range, it is in the transition region between second and third order kinetics and the variation of the rate with total pressure is compared to the behaviour predicted by RRKM theory. Association of OH with NO, OH + NO + M → HNO2+ M, (5), has been studied, but only in its third order range, where k5= 4.1 (±0.6 )× 10–31 cm6 molecule–2 s–1 at 300 K and with M = He; the activation energy =–6.7 (± 2.0) kJ/mol. Some measurements have also been made on the bimolecular reactions, OH + HNO3→ H2O + NO3(11) and O + HNO3→ OH + NO3. (12) At 300 K, k11= 1.3 (± 0.5)× 10–13 cm3 molecule–1 s–1 and k12 < 1.3 × 10–14 cm3 molecule–1 s–1.