A DIODE-LASER STUDY OF THE CL+C2H5 REACTION

Real time IR absorption measurements of the formation Of C2H4 and HCl following the Cl initiated chain reaction between chlorine and ethane are presented. The ethylene molecules, formed by the reaction between chlorine atoms and ethyl radicals, are born highly vibrationally excit ed and are only slowly relaxed in a N2 bath gas. The addition Of C2F6 provides efficient vibrational relaxation and reveals a very fast rise in the ethylene concentration. The measured Cl + C2H5 rare constant i s k3(295 K) = (2.9 +/- 0.6) X 10(-10) cm3 s-1 and resolves a discrepan cy of a factor of 20 in previous reports of this rate constant. Measur ements of the HCI concentration reveal a relatively short chain length under conditions for which the steady-state Cl and C2H5 concentration s are comparable. Fits of the [HCl] time dependence yield a value of k 3 = (3.4 +/- 0.6) x 10(-10) cm3 s-1 for the Cl + C2H5 rate constant, i n agreement with the value derived from the formation of C2H4. We have also measured the rate constant for the addition of chlorine atoms to ethylene and find that k6 = (1.4 +/- 0.2) X 10(-11) and (3.5 +/- 0.7) X 10(-11) cm3 s-1 respectively at 30 and 120 Torr total pressure and 295 K, in good agreement with literature values.