J. Phys. Chem. 1992,96, 303-306
303
Application of Time-Resolved Infrared Spectroscopy to the Determination of Absolute Rate Constants for CI C2Hoand CI 4- C2HSCI
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E. W. Kaiser,* L. Rimai, Scientific Research Laboratories, Ford Motor Company, Mail Drop 3083, Dearborn, Michigan 481 21 -2053
E. Scbwab, and E. C. Lim Department of Chemistry, University of Akron, Akron, Ohio 44325 (Received: July 17, 1991)
Time-resolved infrared spectroscopy (TRISP) has been used to determine at 700 Torr and 298 K the absolute rate constants of reactions (1) C1 + C& = C2HS+ HCl [kl = 7.05 (h1.4) X IO-" cm3/molecule s] and (2) C1 + C2H5Cl= C2H4Cl + HCI [k2 = 6.8 (f1.4) X cm'/molecule SI. Pulsed UV laser photolysis of C12 in flowing mixtures of C12,C2H6 (or C2HSCI),and air initiated the reaction. Absolute rate constants were measured by observing the rate of HCI production using this pulsed, broad-band IR technique for time delays from 50 ns to 10 I.CS after the photolysis laser pulse. Because chain propagation occurs via reactions (4) CzHS C12 = C2H5Cl + C1 or (6) C2H4C1+ C12 = C2H4CI2+ C1, corrections for these reactions were included in the absolute rate calculations. A determination of the rate constant of reaction 6 relative to reaction 5 , C2&Cl + o2= C2&c102, was required to calculate k2. The ratio k6/k, was measured at 700 Torr by continuous UV photolysis of C12,02,and CzHsClmixtures in a static reactor using the relative rate technique. Values of k6/k, = 0.42 (f0.06) and 0.63 (f0.15) were obtained for 1-chloroethyl and 2-chloroethyl radicals, respectively. The measured value of kl agrees with previous low-pressure (
