The rate constant for the reaction C1+ CH, 1 , CH3 + HCl has been determined over the temperature range of 200"-500"K using a discharge flow system with resonance fluorescence detection of atomic chlorine under conditions of large excess CH4. For 300" > 7' > 200°K the data are best fitted to the expression kl = (8.Curvature is observed in the Arrhenius plot such that the effective activation energy increases from 2.6 kcal/mol at 200" < T < 300°K to 3.5 kcal/mol at 360" < T < 500°K. The data over the entire range may be fitted by the expression k l = 8.6 X T2." exp[-795/T]. These results are compared with other experimental studies and with a semiempirical transition state calculation. Their atmospheric significance is discussed.

120 vibrational relaxation rate constants kv,v−1Q are measured at 298 K for HCl (v⩽7) collisions with six diatomics: N2, CO, NO, HCl, DCl, and HF; three triatomics: CO2, N2O, NO2; and eleven polyatomics: CH4, C2H6, C3H8, iso-C4H10, CH3Cl, CH3F, CF4, SF6, CF3Cl, CF2Cl2, and CFCl3. For most quenchers, kQ increases with increasing v independent of whether the vibrational energy gap is reduced or increased. Large collisional relaxation probabilities for high v, of order 0.1 to 1 gas kinetic, are encountered for 11 of 20 quenchers. For Q=HC1 (v=0), the relaxation is shown experimentally to be mainly V–R,T for high v. The rates reflect a mix of effects due to dipole and dispersion interactions, energy gap, rotation, and complex formation, and present interesting problems of interpretation.

The infrared chemiluminescence method of Smith and co-workers is adapted to fast flow reactor conditions where a sensitive infrared detector views the vibrationally excited products of various generating reactions through a circularly variable filter in the absence or presence of added quencher molecules. The initial vdistributions are found to be totally unrelaxed vibrationally but thermalized rotationally. This allows the experimental measurement of vibrational relaxation rates of high v levels hitherto inaccessible. The modified Stern-Volmer method of analysis is described in detail. Its reference process is the rapid pumping rate constant < 5 X 10 3 S-l out of the field of view. HCI t is generated by anyone of four H atom reactions (with CI" ICI, CINO, or SOCI,) or two CI atom reactions (with HI or HBr), and its quenching rates by CO, or N,o are measured. Quenching probabilities from about 5 X 10-3 to 0.5 per gas-kinetic collisions for v = I to 7 are found for both gases. The results are compared with the limited published data. Detailed discussion is deferred until the following paper which presents data for 18 additional quenchers.2972