Rate coefficients and mechanisms of the reaction of Cl-atoms with a series of unsaturated hydrocarbons under atmospheric conditions

Rate coefficients and/or mechanistic information are provided for the reaction of Cl-atoms with a number of unsaturated species, including isoprene, methacrolein (MAC R), m ethyl vinyl ketone (MVK), 1,3-butadiene, trans-2-butene, and 1-butene. The following Cl-atom rate coefficients were obtained at 298 K near 1 atm total pressure: k(isoprene) = (4.3 +/- 0.6) x 10(-10) cm(3) molecule(-1) s(-1) (independent of pressure from 6.2 to 760 Torr); k(MVK) (2.2 +/- 0.3) x 10(-10) cm(3) molecule(-1) s(-1), k(MACR) = (2.4 +/- 0.3) x 10(-10) cm(3) molecule(-1) k(trans-2-butene) = (4.0 +/- 0.5) x 10(-10) cm(3) molecule(-1) s(-1), k(1-butene) = (3.0 +/- 0.4) x 10(-10) cm(3) molecule(-1) s(-1). Products observed in the Cl-atom-initiated oxidation of the unsaturated species at 298 K in 1 atm air are as follows (with % molar yields in parentheses): CH2O (9.5 +/- 1.0%), HCOCl (5.1 +/- 0.7%), and 1-chloro-3-methyl-3-buten-2-one (CMBO, not quantihed) from isoprene; chloroacetalclehyde (75 +/- 8%), CO2 (58 +/- 5%), CH2O (47 +/- 7%), CH3OH (8%), HCOCl (7 +/- 1%), and peracetic acid (6%) from MVK; CO (52 +/- 4%), chloroacetone (42 +/- 5%), CO2 (23 +/- 2%), CH2O (18 +/- 2%), and HCOCl (5%) from MACR; CH2O (7 +/- 1%), HCOCl (3%), acrotein (53%), and 4-chlorocrotonaldehyde (CCA, not quantihed) from 1,3-butadiene; CH3CHO (22 +/- 3%), CO2 (13 +/- 2%), 3-chloro-2-butanone (13 +/- 4%), CH2O (7.6 1. 1%), and CH3OH (1.8 +/- 0.6%) from trans-2-butene, and chloroacetaldehyde (20 3%), CH2O (7 +/- 1%), CO2 (4 +/- 1%), and HCOCl (4 +/- 1%) from 1-butene. Product yields from both trans-2-butene and 1-butene were found to be O-2-dependent, in the case of trans-2-butene, the observed O-2-dependence is the result of a competition between unimolecular decomposition of the CH3CH(Cl)-CH(O-)-CH3 radical and its reaction with O-2, with k(decomp)/kO(2) = (1.6 +/- 0.4) x 10(19) molecule cm(-3). The activation energy for decomposition is estimated at 11.5 +/- 1.5 kcal mol(-1). The variation of the product yields with 02 in the case of I-butene results from similar competitive reaction pathways for the two beta-chlorobutoxy radicals involved in the oxidation, ClCH2CH(O-)CH2CH3 and -OCH2CHClCH2CH3. (C) 2003 Wiley Periodicals, Inc.