Atmospheric Chemistry of Cyclohexane: UV Spectra of c-C6H11• and (c-C6H11)O2• Radicals, Kinetics of the Reactions of (c-C6H11)O2• Radicals with NO and NO2, and the Fate of the Alkoxy Radical (c-C6H11)O•

Abstract

A pulse radiolysis technique was used to measure the UV absorption spectra of c-C6H11• and (c-C6H11)O2• radicals over the ranges 230−290 and 220−300 nm, σ(c-C6H11•)250 nm = (7.0 ± 0.8) × 10-18 and σ((c-C6H11)O2•)250 nm = (5.7 ± 0.6) × 10-18 cm2 molecule-1. The rate constant for the self-reaction of c-C6H11• radicals was k3 = (3.0 ± 0.4) × 10-11 cm3 molecule-1 s-1. The addition reaction of c-C6H11• radicals with O2 proceeds with a rate constant k2 = (1.3 ± 0.2) × 10-11 cm3 molecule-1 s-1. Rate constants for reactions of (c-C6H11)O2• radicals with NO and NO2 were k4 = (6.7 ± 0.9) × 10-12 and k5 = (9.5 ± 1.5) × 10-12 cm3 molecule-1 s-1, respectively. FTIR−smog chamber techniques were used to record the IR spectrum of the peroxynitrate (c-C6H11)O2NO2, determine that the reaction between (c-C6H11)O2• radicals and NO produces a (16 ± 4)% yield of the nitrate (c-C6H11)ONO2, and study the atmospheric fate of cyclohexoxy radicals. Decomposition via C−C bond scission and reaction with O2 are competing fates of the cyclohexoxy radical. In 700−750 Torr total pressure at 296 ± 2K, the rate constant ratio kdecomp/kO2 = (8.1 ± 1.5) × 1018 molecule cm-3. At 296 K in 1 atm of air, 61% of cyclohexoxy radicals decompose and 39% react with O2. These results are discussed with respect to the literature data concerning the atmospheric chemistry of cyclohexane and analogous compounds.