Rate coefficients and/or mechanistic information are provided for the reaction of Cl‐atoms with a number of unsaturated species, including isoprene, methacrolein ( MACR ), methyl 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) × 10
?10cm
3 molecule
?1 s
?1 (independent of pressure from 6.2 to 760 Torr);
k( MVK ) = (2.2 ± 0.3) × 10
?10 cm
3 molecule
?1 s
?1;
k( MACR ) = (2.4 ± 0.3) × 10
?10 cm
3 molecule
?1 s
?1;
k(
trans‐2‐butene) = (4.0 ± 0.5) × 10
?10 cm
3 molecule
?1 s
?1;
k(1‐butene) = (3.0 ± 0.4) × 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): CH
2O (9.5 ± 1.0%), HCOCl (5.1 ± 0.7%), and 1‐chloro‐3‐methyl‐3‐buten‐2‐one (CMBO, not quantified) from isoprene; chloroacetaldehyde (75 ± 8%), CO
2 (58 ± 5%), CH
2O (47 ± 7%), CH
3OH (8%), HCOCl (7 ± 1%), and peracetic acid (6%) from MVK ; CO (52 ± 4%), chloroacetone (42 ± 5%), CO
2 (23 ± 2%), CH
2O (18 ± 2%), and HCOCl (5%) from MACR ; CH
2O (7 ± 1%), HCOCl (3%), acrolein (≈3%), and 4‐chlorocrotonaldehyde (CCA, not quantified) from 1,3‐butadiene; CH
3CHO (22 ± 3%), CO
2 (13 ± 2%), 3‐chloro‐2‐butanone (13 ± 4%), CH
2O (7.6 ± 1.1%), and CH
3OH (1.8 ± 0.6%) from
trans‐2‐butene; and chloroacetaldehyde (20 ± 3%), CH
2O (7 ± 1%), CO
2 (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 CH
3CH(Cl)? CH(O?)? CH
3 radical and its reaction with O
2, with
kdecomp/
kO2 = (1.6 ± 0.4) × 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 O
2 in the case of 1‐butene results from similar competitive reaction pathways for the two β‐chlorobutoxy radicals involved in the oxidation, ClCH
2CH(O?)CH
2CH
3 and ?OCH
2CHClCH
2CH
3. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 334–353, 2003
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