Kinetics of CH₂ClO Radical Reactions with O₂ and NO, and the Unimolecular Elimination of HCl

Abstract

The kinetics of the title reactions were investigated at 5−35 Torr total pressure and 265−306 K by UV flash photolysis and time-resolved mass spectrometry. The CH2ClO radical was generated by photolysis of NOCl in the presence of CH3Cl, O2, and NO. Atomic chlorine from NOCl photodissociation abstracted H from CH3Cl and initiated oxidation of CH2Cl radicals, leading to formation of CH2ClO. The CH2ClO radical reacted with both O2 and NO, or underwent unimolecular elimination of HCl. The kinetics were determined from growth rates of HC(O)Cl and HCl. The rate coefficient of the CH2ClO + O2 reaction was found to be independent of pressure. The temperature dependence can be expressed as: k(CH2ClO + O2) = (2.0 ± 0.7) × 10-12 exp[−(934 ± 128)/T] cm3 molecule-1 s-1. The rate coefficients for the CH2ClO + NO reaction were found to be independent of both pressure and temperature, with the value k(CH2ClO + NO) = (2.7 ± 0.6) × 10-12 cm3 molecule-1 s-1, obtained by averaging all rate coefficients determined over the experimental range of pressure and temperature. The rate coefficient for unimolecular elimination of HCl from CH2ClO was found to be pressure dependent, and well into the falloff. The unimolecular rate coefficient at 10 Torr can be expressed as (7.7 ± 2.3) × 109 exp[−(4803 ± 722)/T] s-1.