Reactions of alkoxy radicals under atmospheric conditions: The relative importance of decomposition versus reaction with O2

Abstract

The reactions of alkoxy radicals determine to a large extent the products formed during the atmospheric degradations of emitted organic compounds. Experimental data concerning the decompositions, 1,5-H shift isomerizations and reactions with O 2 of several classes of alkoxy radicals are inconsistent with literature estimations of their absolute or relative rate constants. An alternative, although empirical, method for assessing the relative importance under atmospheric conditions of the reactions of alkoxy radicals with 02 versus decomposition was derived. This estimation method utilizes the differences in the heats of reaction, A(AH) = (AH d .... position -AHo,,,actioo), between these two reactions pathways. For A(AH)~ [22-0.5(AHo ...... io,)], alkoxy radical decomposition dominates over the reaction with 02 at room temperature and atmospheric pressure of air, while for A(AH) -> [25 --0.5(AH O .... tion)], the 02 reaction dominates over decomposition (where the units of AH are in kcal mol-t). The utility and shortcomings of this approach are discussed. It is concluded that further studies concerning the reactions of alkoxy radicals are needed.

FTIR study of the Cl- and Br-atom initiated oxidation of trichloroethylene

“…3), the conversion of CHCl " CCl 2 (9.02 mtorr) was greater than twice the initial concentration of Cl 2 (4 mtorr) providing further evidence for the presence of this second source of chlorine atoms. C 9 C bond scission is also a possibility for the decomposition of ethoxy radicals [25] such as CHCl 2 9 CCl 2 O:…”

Theoretical calculation of activation energy barrier from vibrational frequencies for the reaction of O (3P) with CHFCl

“…Table II shows that the energetically most favorable reaction path is IM1 3 Cl ϩ CHFO via bond cleavage transition state TS1, which does not involve an activation process, and the calculated energy is 0.88 compared to 0.4 kcal/mol 1 . The accounted barrier of the second reaction channel is 18.11 kcal/mol 1 , but the IM1 is activated from 2 S 1/2 to 2 P 1/2 or from v ϭ 0 to v ϭ 1.…”

“…The accounted barrier of the second reaction channel is 18.11 kcal/mol 1 , but the IM1 is activated from 2 S 1/2 to 2 P 1/2 or from v ϭ 0 to v ϭ 1. The calculated energy for the next channel by TS3 is 27.92 kcal/ mol 1 . The HF elimination reaction channel forming HF ϩ ClCO via three-centered transition state TS4 has the highest potential energy on the potential energy surface of IM1 (21.02 to 21.55 kcal/mol 1 ), and the IM1 is activated from 2 S 1/2 to 2 D 3/2 , i.e., from v ϭ 0 to v ϭ 3.…”

“…In the troposphere, CH 2 ClF, which is insoluble in water and volatile in nature, will react with the hydroxyl and produce CHClF radicals [1,2]. The CHClF radicals can combine with O ( 3 P) atoms [3][4][5] and form chlorofluoromethoxy radicals, but the latter can give out the Cl atoms to destroy ozone through a series of chain reactions.…”

Trichloroethene and tetrachloroethene: tropospheric probes for Cl- and Br-atom reactions during the polar sunrise

“…Thus, in reaction (3a), Cl-atoms are regenerated, leading to a chain reaction consuming the initial reactants. The breakage of the C-C bond is also a possibility (Atkinson and Carter, 1991) for the decomposition of ethoxy radicals produced in reaction (2), forming CClzO and CXCl z . The latter would rapidly associate with Oz (Niki et aI., 1980).…”