Degradation of three oxygenated alkoxy radicals of atmospheric interest: HOCH2O˙, CH3OCH2O˙, CH3OCH2OCH2O˙. RRKM theoretical study of the β-C–H bond scission and the 1,6-isomerisation kinetics

Abstract

A detailed theoretical study on the pressure and temperature dependence of the rate constants k₁, k₂, k₃ for the thermal β-C–H dissociation of the three radicals: HOCH₂O˙, CH₃OCH₂O˙, CH₃OCH₂OCH₂O˙ is presented. This investigation is extended to the rate constant k₄ for the 1,6-H-shift isomerisation of CH₃OCH₂OCH₂O˙. High-level ab initio computations (CCSD(T)//MP2) have been performed and combined with RRKM theory to obtain rate constants. The β-C–H scission pathway is predicted to occur with an activation energy of 10–13 kcal mol⁻¹. Estimation of the competition between the β-C–H and β-C–O decompositions, the isomerisation process, and the reaction with oxygen has been done. At 760 Torr and 298 K, k₁, k₂, k₃, k₄ are 4.4 × 10⁴ s⁻¹, 5.2 × 10⁴ s⁻¹, 4.2 × 10³ s⁻¹ and 5.6 × 10³ s⁻¹ respectively. An interesting result is that the isomerisation through a seven-membered transition state may compete with the H-atom elimination from the CH₃OCH₂OCH₂O˙ radical.