INFRARED-ABSORPTION PROBING OF THE CL- RATE COEFFICIENT FOR HCL PRODUCTION BETWEEN 290-K AND 800-K(C3H6 REACTION )

The reaction of Cl with propylene, C3H6, has been investigated as a fu nction of temperature (293-800 K) and pressure (3-10 Torr) using the l aser photolysis/infrared long-path absorption (LP/IRLPA) technique. Th e measured rate coefficient for HCl production is well-described by a simple Arrhenius expression (4.9 +/- 0.5) x 10(-11) exp[-(90 +/- 50)/T ] cm(3) molecule(-1) s(-1) (all error estimates +/- 2 sigma). At T les s than or equal to 400 K biexponential time behavior of the HCl produc tion is observed, arising from excited C3H6Cl adduct dissociation, but at higher temperature single-exponential behavior is seen. Comparison of measurements in CO2. buffer, where HCl vibrational relaxation is r apid, and in Ar buffer allows extraction of the HCl(upsilon = 1) + C3H 6 vibrational relaxation rate and the fraction of vibrationally excite d HCl produced in the reaction. The measured rate coefficient for HCl( upsilon=1) vibrational relaxation by C3H6 is (3.7 +/- 0.7) x 10(-12) c m(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 smal ler contribution from addition-elimination.