KINETICS AND MECHANISMS OF THE REACTIONS OF CHLORINE ATOMS WITH ETHANE, PROPANE, AND N-BUTANE

Absolute (flash photolysis) and relative (FTIR-smog chamber and GC) ra te techniques were used to study the gas-phase reactions of Cl atoms w ith C2H6 (k(1)), C3H8 (k(3)), and n-C4H10 (k(2)). At 297+/-1K the resu lts from the two relative rate techniques can be combined to give k(2) /k(1)=(3.76+/-0.20) and k(3)/k(1)=(2.42+/-0.10). Experiments performed at 298-540 K give k(2)/k(1)=(2.0+/-0.1)exp((183+/-20)/T). At 296 K th e reaction of Cl atoms with C3H8 produces yields of 43+/-3% 1-propyl a nd 57+/-3% 2-propyl radicals, while the reaction of Cl atoms with n-C4 H10 produces 29+/-2% 1-butyl and 71+/-2% 2-butyl radicals. At 298 K an d 10-700 torr of N-2 diluent, 1- and 2-butyl radicals were found to re act with Cl-2 with rate coefficients which are 3.1+/-0.2 and 2.8+/-0.1 times greater than the corresponding reactions with O-2. A flash-phot olysis technique was used to measure k(1)=(5.75+/-0.45)x10(-11) and k( 2)=(2.15+/-0.15)x10(-10) cm(3) molecule(-1) s(-1) at 298 K, giving a r ate coefficient ratio k(2)/k(1)=3.74+/-0.40, in excellent agreement wi th the relative rate studies. The present results are used to put othe r, relative rate measurements of the reactions of chlorine atoms with alkanes on an absolute basis. It is found that the rate of hydrogen ab straction from a methyl group is not influenced by neighboring groups. The results are used to refine empirical approaches to predicting the reactivity of Cl atoms towards hydrocarbons. Finally, relative rate m ethods were used to measure rate coefficients at 298 K for the reactio n of Cl atoms with 1- and 2-chloropropane and 1- and 2-chlorobutane of (4.8+/-0.3)x10(-11), (2.0+/-0.1)x10(-10), (1.1+/-0.2)x10(-10), and (7 .0+/-0.8)x10(-11) cm(3) molecule(-1) s(-1), respectively. (C) 1997 Joh n Wiley & Sons, Inc.