APPLICATION OF TIME-RESOLVED INFRARED-SPECTROSCOPY TO THE DETERMINATION OF ABSOLUTE RATE CONSTANTS FOR CL+C2H6 AND CL+C2H5CL

Time-resolved infrared spectroscopy (TRISP) has been used to determine at 700 Torr and 298 K the absolute rate constants of reactions (1) Cl + C2H6 = C2H5 + HCl [k1 = 7.05 (+/- 1.4) x 10(-11) cm3/molecule s] and (2) Cl + C2H5Cl = C2H4Cl + HCl [k2 = 6.8 (+/- 1.4) x 10(-12) cm3/molecule s]. Pulsed UV laser photolysis of Cl2 in flowing mixtures of Cl2, C2H6 (or C2H5Cl), and air initiated the reaction. Absolute rate constants were measured by observing the rate of HCl production using this pulsed, broad-band IR technique for time delays from 50 ns to 10-mu-s after the photolysis laser pulse. Because chain propagation occurs via reactions (4) C2H5 + Cl2 = C2H5Cl + Cl or (6) C2H4Cl + Cl2 = C2H4Cl2 + Cl, corrections for these reactions were included in the absolute rate calculations. A determination of the rate constant of reaction 6 relative to reaction 5, C2H4Cl + O2 = C2H4ClO2, was required to calculate k2. The ratio k6/k5 was measured at 700 Torr by continuous UV photolysis of Cl2, O2, and C2H5Cl mixtures in a static reactor using the relative rate technique. Values of k6/k5 = 0.42 (+/- 0.06) and 0.63 (+/- 0.15) were obtained for 1-chloroethyl and 2-chloroethyl radicals, respectively. The measured value of k1 agrees with previous low-pressure (< Torr) determinations verifying that reaction 1 is pressure independent.