Kinetics of chlorine oxide radical reactions using modulated photolysis. Part 3.—Pressure and temperature dependence of the reaction: ClO + NO2(+ M)→ ClONO2(+ M)

Abstract

The pressure and temperature dependence of the rate constant for the reaction ClO + NO₂(+ N₂)→ ClONO₂(+ N₂) has been studied using the technique of modulated photolysis–u.v. absorption spectrometry to follow ClO radical kinetics. The temperature range was 274–339 K and the pressure range 25–612 Torr. At 50 Torr the experimental values of the rate constant expressed in Arrhenius form were given by k₁=(4.3 ± 1.2)× 10^–33 exp[(1085 ± 86)/T] cm⁶ molecule^–2 s^–1 which agrees closely with the consensus mean value for the termolecular rate constant obtained from previous studies at low pressure (≲ 4 Torr). At pressures > 50 Torr, the expected fall-off behaviour for association reactions of this type was observed.