Kinetics of gas‐phase reactions of CH₃OCH₂CF₃, CH₃OCH₃, CH₃OCH₂CH₃, CH₃CH₂OCH₂CH₃, and CHF₂CF₂OCH₂CF₃ with NO₃ radicals at 298 K

Abstract

Abstract Rate constants for the gas‐phase reactions of CH 3 OCH 2 CF 3 ( k 1 ), CH 3 OCH 3 ( k 2 ), CH 3 OCH 2 CH 3 ( k 3 ), and CH 3 CH 2 OCH 2 CH 3 ( k 4 ) with NO 3 radicals were determined by means of a relative rate method at 298 K. NO 3 radicals were prepared by thermal decomposition of N 2 O 5 in a 700–750 Torr N 2 O 5 /NO 2 /NO 3 /air gas mixture in a 1‐m 3 temperature‐controlled chamber. The measured rate constants at 298 K were k 1 = (5.3 ± 0.9) × 10 −18 , k 2 = (1.07 ± 0.10) × 10 −16 , k 3 = (7.81 ± 0.36) × 10 −16 , and k 4 = (2.80 ± 0.10) × 10 −15 cm 3 molecule −1 s −1 . Potential energy surfaces for the NO 3 radical reactions were computationally explored, and the rate constants of k 1 – k 5 were calculated according to the transition state theory. The calculated values of rate constants k 1 – k 4 were in reasonable agreement with the experimentally determined values. The calculated value of k 5 was compared with the estimate ( k 5 < 5.3 × 10 −21 cm 3 molecule −1 s −1 ) derived from the correlation between the rate constants for reactions with NO 3 radicals ( k 1 – k 4 ) and the corresponding rate constants for reactions with OH radicals. We estimated the tropospheric lifetimes of CH 3 OCH 2 CF 3 and CHF 2 CF 2 OCH 2 CF 3 to be 240 and >2.4 × 10 5 years, respectively, with respect to reaction with NO 3 radicals. The tropospheric lifetimes of these compounds are much shorter with respect to the OH reaction. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 490–497, 2009