A kinetic study of the CH2OO Criegee intermediate reaction with SO2, (H2O)2, CH2I2 and I atoms using OH laser induced fluorescence

Abstract

The OH laser induced fluorescence method was used to study the kinetics of CH₂OO reacting with SO₂, (H₂O)₂, CH₂I₂ and I atoms. Decay of CH₂OO is not strictly first-order since its self-reaction is rapid. With this consideration, we derived the rate coefficient of CH₂OO + SO₂/(H₂O)₂/CH₂I₂/I taking into account the contribution of the CH₂OO self-reaction. For the CH₂OO + SO₂ reaction, the rate coefficient is measured to be (3.88 ± 0.13) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at 10 Torr, which agrees very well with a previously reported value obtained by directly monitoring CH₂OO using the UV absorption method with the CH₂OO self-reaction considered. We did not observe obvious evidence for SO₂ catalysed CH₂OO isomerization or the intersystem crossing effect in this reaction. CH₂OO + (H₂O)₂ is supposed to account for the major sink of CH₂OO in the atmosphere, but previous rate coefficient measurements were not in good agreement. We have revisited this reaction including the self-reaction of CH₂OO and obtained the rate coefficient to be (7.53 ± 0.38) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ at 60 Torr and 300 K. The rate coefficients of CH₂OO + CH₂I₂ and CH₂OO + I were measured to be (5.2 ± 2.6) × 10⁻¹⁴ and (2.2 ± 1.1) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ respectively.