KINETICS OF CL ATOM REACTIONS WITH C2H6, C2H5, AND C2H4 RATES OF DISPROPORTIONATION AND RECOMBINATION OF ETHYL RADICALS

The kinetics of Cl atom reaction with ethane at 298 K were studied with the very low pressure reactor (VLPR). In the very early stages of reaction, with [Cl] > [C2H6], there is a very fast and irreversible reaction (1), producing HCl + C2H5 followed by a slightly slower reaction (2) of Cl with C2H5 to produce HCl + C2H4. An extremely slow reaction (4) of Cl with C2H4 to form HCl + C2H3 can also be seen followed by a much faster reaction (5) of Cl with C2H3 to form HCl + C2H2. After 50% Cl conversion when [Cl] < [C2H6], only reactions 1 and 3 (the disproportionation of C2H5) are important. By studying the reaction over large ranges of concentration of both Cl and C2H6, it is possible to obtain all rate constants except for (5) with good accuracy (cm3/molecule·s ⨯ 1011): k1 = 6.10 ± 0.11, k2 = 1.21 ± 0.04, k3 = 0.227 ± 0.006, k4 = 0.050 ± 0.002. Reaction 2 occurs via an initial recombination that is rate determining and can be described by the recently modified Gorin model for recombination. Ethyl radical disproportionation (3) is well described by a contact-transition-state model. From k3 and the known ratio for disproportionation to recombination of 0.14 ± 0.01, the rate of recombination of ethyl radical at 298 K is calculated as kT = (1-62 ± 0.14) ⨯ 10-11 cm3/molecule·s = (9.7 ± 0.8) ⨯ 109 L/mol·s. © 1990, American Chemical Society. All rights reserved.