Gas-phase reactions of hydroxyl radicals with alkyl nitrite vapours in H2O2+ NO2+ CO mixtures

Abstract

The yields of CO₂ from the chain reaction in H₂O₂+ NO₂+ CO + alkyl nitrite mixtures, in which OH is the chain carrier and alkyl nitrites induce a chain termination step, have been used to deduce rate constants (k_s) for OH attack on alkyl nitrites (RONO) in the vapour phase at ambient temperatures. Values of k_s/10⁹ dm³ mol^–1 s^–1 as a function of R were determined as follows: 0.71 ± 0.12 (CH₃), 1.15 ± 0.23 (C₂H₅), 1.56 ± 0.32 (n-C₃H₇), 3.41 ± 1.48 (n-C₄H₉), 3.89 ± 0.58 (sec-C₄H₉), 3.47 ± 0.52 (i-C₄H₉), 0.91 ± 0.15 (t-C₄H₉), all based on k_s=(1.63 ± 0.16)× 10⁹ dm³ mol^–1 s^–1 for OH + n-butane. The small increase in k_s from R = CH₃ to t-C₄H₉ is considered to support a recent postulate that both H-abstraction and NO-abstraction pathways are operative, at least for R = CH₃.

Under typical, sunlit urban atmosphere conditions it is deduced that OH attack on alkyl nitrites is a minor removal process compared to their photodissociative destruction.