Kinetics and product of the gas-phase reaction of ClO with NO2

Abstract

The association reaction of ClO with NO₂ has been studied by infrared absorption spectroscopy and molecular modulation spectroscopy. Photolysis of OClO–NO₂–N₂ mixtures produced ClO radicals over a wide range of reagent concentrations at 303 K, and total pressures of 10 and 25 Torr and 1 atm. The major product of the association reaction was chlorine nitrate, ClONO₂, with no evidence for the formation of any other isomers.

Observation of the kinetics of OClO removal, ClONO₂ formation and the transient behaviour of ClO are consistent with the following reactions: ClO + NO₂+ M → ClONO₂+ M. (1), OClO +hν→ ClO + O (2), O + NO₂→ NO + O₂(3), OClO + NO → ClO + NO₂. (4) The third-order rate coefficient, k₁, measured from the photolysis of mixtures of [OClO] < 10¹⁴ molecule cm^–3 was 1.40 ± 0.07 × 10^–31 cm⁶ molecule^–2 s^–1, in good agreement with previous reports; however, k₁ appeared to decline with increasing OClO concentration. This apparent decline is difficult to rationalize on the basis of existing knowledge.