Infrared Absorption Probing of the Cl + C3H6 Reaction: Rate Coefficients for HCl Production between 290 and 800 K

The reaction of Cl with propylene, C 3 H 6, has been investigated as a function of temperature (293−800 K) and pressure (3−10 Torr) using the laser photolysis/infrared long-path absorption (LP/IRLPA) technique. The measured rate coefficient for HCl production is well-described by a simple Arrhenius expression (4.9 ± 0.5) × 10 -11 exp[−(90 ± 50)/T] cm 3 molecule -1 s -1 (all error estimates ± 2σ). At T ≤ 400 K biexponential time behavior of the HCl production is observed, arising from excited C 3 H 6 Cl adduct dissociation, but at higher temperature single-exponential behavior is seen. Comparison of measurements in CO 2 buffer, where HCl vibrational relaxation is rapid, and in Ar buffer allows extraction of the HCl( v =1) + C 3 H 6 vibrational relaxation rate and the fraction of vibrationally excited HCl produced in the reaction. The measured rate coefficient for HCl( v =1) vibrational relaxation by C 3 H 6 is (3.7 ± 0.7) × 10 -12 cm 3 molecule -1 s -1, and the fraction of vibrationally excited HCl produced in the reaction is 0.48 ± 0.06 at 293 K. The observations are consistent with a dominant direct abstraction mechanism and a smaller contribution from addition−elimination.