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

Unimolecular decomposition kinetics of the stabilised Criegee intermediates CH2OO and CD2OO

“…At 450 K, the data suggest a contribution from reaction between CH 2 OO and CH 2 I 2 (see ESI †), with a bimolecular rate coefficient of (8.2 AE 1.7) Â 10 À12 cm 3 s À1 . The reaction has also recently been observed by Liu et al, 17 with a rate coefficient of (5.2 AE 2.6) Â 10 À14 cm 3 s À1 at 298 K. At temperatures above 450 K, concentrations of CH 2 I 2 were not varied over a sufficient range to fully assess the role of CH 2 OO + CH 2 I 2 ; however, the results overall are consistent with the pressure-independent loss term at all temperatures coming largely from the pseudo-first-order loss of CH 2 OO through reaction with CH 2 I 2 .…”

“…There was little variation in the product distribution over the pressure and temperature ranges investigated, with yields of 63.7% for H 2 + CO 2 and 36.0% for H 2 O + CO, on average. The yields of OH + HCO is predicted to be 0.3%, on average, and is lower than the estimates based on the OH measurements reported in this work and those indicated by the use of OH as a proxy to CH 2 OO in experiments by Liu et al 16 and Li et al 17 The optimised TS2 energy and hDEi down were also used in MESMER simulations to calculate k 1 at temperatures between 200 K and 850 K and pressures up to 10 atm. The calculated rate coefficients were subsequently parameterised using the Troe expression for broad falloff curves 53 (eqn (7)-(9)) for use in kinetic models:…”

“…14,15 Experimental evidence for OH production from CH 2 OO also comes from studies in which the behaviour of OH radicals has been probed following the photolysis of CH 2 I 2 in O 2 /Ar gas mixtures. 16,17 These studies have successfully used OH measurements as proxies to determine the kinetics of CH 2 OO reactions, including with SO 2 . This finding implicates the decomposition of stabilised CH 2 OO as the OH radical source, although decomposition kinetics were not directly probed.…”

“…This finding implicates the decomposition of stabilised CH 2 OO as the OH radical source, although decomposition kinetics were not directly probed. 16,17 Similarly, a study of SCIs generated by alkene ozonolysis has also identified the decomposition of stabilised CH 2 OO as a potential source of OH, but kinetic information was limited and a low OH yield was reported. 18 Ozonolysis experiments performed in atmospheric simulation chambers have been used to infer the kinetics of stabilised CH 2 OO decomposition, but with large uncertainties, since firstorder losses of CH 2 OO by physical processes such as wall reactions are difficult to distinguish from loss through unimolecular decomposition.…”

Criegee intermediates and their impacts on the troposphere

“…ƒ the values from the experiments could not distinguish between the reaction with the water monomer or the dimer reaction. Lin et al 52 Ryzhkov and Ariya 55 Liu et al 62 Chao et al 58 Smith et al 63 Lewis et al 64 Yajima et al 65 Sheps et al 50…”