Effects of Water Vapor on the Kinetics of the Methylperoxy Radical Self-reaction and Reaction with Hydroperoxy

• Main Author: Mower, Alecia
• Format: Others
• Published: BYU ScholarsArchive 2007
• Subjects: kinetics; methylperoxy; hydroperoxy; CH302; HO2; Biochemistry; Chemistry
• Online Access: https://scholarsarchive.byu.edu/etd/1252; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=2251&context=etd

The gas phase reactions of CH3O2 + CH3O2, HO2 + HO2, and CH3O2 + HO2 in the presence of water vapor have been studied at temperatures between 263 and 303 K using laser flash photolysis coupled with UV time-resolved absorption detection at 220 nm and 260 nm. Water vapor concentration was quantified using tunable diode laser spectroscopy operating in the mid-IR. The HO2 self-reaction rate constant is significantly enhanced by water vapor, consistent with what others have reported, whereas CH3O2 self-reaction and the cross-reaction (CH3O2 + HO2) rate constants are nearly unaffected. The enhancement in the HO2 self-reaction rate coefficient occurs because of the formation of a strongly bound (6.9 kcal mol-1) HO2-H2O complex during the reaction mechanism where the H2O acts as an energy chaperone. The nominal impact of water vapor on the CH3O2 self-reaction rate coefficient is consistent with recent high level ab initio calculations that predict a weakly bound CH3O2-H2O complex (3.2 kcal mol-1). The smaller binding energy of the CH3O2-H2O complex excludes its formation and consequent participation in the methyl peroxy self-reaction mechanism.