Pressure-Dependent Kinetics of the Reaction between CH₃O₂ and OH: TRIOX Formation

Reaction of methyl peroxy radicals with hydroxyl radicals (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy at 296 K over the 1-100 bar pressure range (bath gas He): CH₃O₂ + OH → CH₃O + HO₂ (1a), CH₃O₂ + OH → CH₂OO + H₂O (1b), and CH₃O₂ + OH → CH₃OOOH (TRIOX) (1d). Channel 1a is the dominant channel under ambient conditions, while the contribution of channel 1b is less than 5% at 1 bar and 296 K. Channel 1c is strongly pressure-dependent and becomes dominant at high pressures. The measured branching ratio of channel 1c is α_1c = 0.87 ± 0.20 at 100 bar and 296 K. The chain termination channel 1c forming important product TRIOX is experimentally evaluated over an extended pressure range (1-100 bar) for the first time. The stabilization channel 1c might play a role at ambient pressures and low temperatures as well as high pressures at ambient and elevated temperatures.