A laser flash photolysis/IR diode laser absorption study of the reaction of chlorine atoms with selected alkanes

A high‐resolution IR diode laser in conjunction with a Herriot multiple reflection flow‐cell has been used to directly determine the rate coefficients for simple alkanes with Cl atoms at room temperature (298 K). The following results were obtained: k (Cl + n‐butane) = (1.91 ± 0.10) × 10 −10 cm 3 molecule −1 s −1 , k (Cl + n ‐pentane) = (2.46 ± 0.12) × 10 −10 cm 3 molecule −1 s −1 , k (Cl + iso‐pentane) = (1.94 ± 0.10) × 10 −10 cm 3 molecule −1 s −1 , k (Cl + neopentane) = (1.01 ± 0.05) × 10 −10 cm 3 molecule −1 s −1 , k (Cl + n ‐hexane) = (3.44 ± 0.17) × 10 −10 cm 3 molecule −1 s −1 where the error limits are ±1σ. These values have been used in conjunction with our own previous measurements on Cl + ethane and literature values on Cl + propane and Cl + iso‐butane to generate a structure activity relationship (SAR) for Cl atom abstraction reactions based on direct measurements. The resulting best fit parameters are k p = (2.61 ± 0.12) × 10 −11 cm 3 molecule −1 s −1 , k s = (8.40 ± 0.60) × 10 −11 cm 3 molecule −1 s −1 , k t = (5.90 ± 0.30) × 10 −11 cm 3 molecule −1 s −1 , with f ( CH 2 ) = f ( CH 2 ) = f (C) = f = 0.85 ± 0.06. Tests were carried out to investigate the potential interference from production of excited state HCl( v = 1) in the Cl + alkane reactions. There is some evidence for HCl( v = 1) production in the reaction of Cl with shape n ‐hexane. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 86–94, 2002