Rate measurements of reactions of OH by resonance absorption. Part 5.—Rate constants for OH + NO2(+M)→ HNO3(+M) over a wide range of temperature and pressure

Abstract

The kinetics of the reaction OH + NO₂(+M)→ HNO₃(+M) have been studied, using flash photolysis to generate OH radicals and time-resolved resonance absorption to observe the rate of their removal. Effective second-order rate constants, k₁=(–d ln [OH]/dt)/[NO₂], have been determined for the ranges: 220 ⩽T⩽ 550 K and 3.2 × 10¹⁷⩽[M]⩽ 1.6 × 10¹⁹ molecule cm^–3. In this range of [M] the kinetics are in the changeover region between third- and second-order, but values of limiting low and high pressure rate constants have been found using an interpolation procedure due to Troe. Most of the experiments have been carried out with M = N₂ but results have also been obtained with M = He, Ar, O₂ and SF₆.