The kinetics of the disproportionation reactions of OH and OD radicals, OH + OH → O + H2O (1), OD + OD → O + D2O (3), have been studied by the mass spectrometric discharge-flow method at temperatures between 233 and 360 K and at total pressure of 1 Torr of helium. The following Arrhenius expressions were obtained:  k 1 = (7.1 ± 1.0) × 10-13exp[(210 ± 40)/T] and k 3 = (2.5 ± 0.5) × 10-13exp[(170 ± 60)/T] cm3 molecule-1 s-1. Reaction 4 between OH and OD radicals was also investigated and the same rate constant as for reaction 1 was measured. Both the observed temperature dependence of k 1 and the measured kinetic isotopic effect (k 1/k 3) are compatible with the mechanism proposed in a previous theoretical study (Harding, L. B.; Wagner, A. F. 22nd International Symposium on Combustion, 1988). In addition, a temperature-independent rate coefficient of (1.20 ± 0.25) × 10-10 cm3 molecule-1 s-1 was measured for the reaction D + NO2 → OD + NO in the temperature range 230−365 K.

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The kinetics of the reaction of chlorine atoms with isoprene (1) has been studied using the discharge-flow mass-spectrometric method: Cl + C 5 H 8 (+M) f C 5 H 8 Cl (+M) (1a); Cl + C 5 H 8 f C 5 H 7 + HCl (1b). As a result of direct and relative measurements, the overall rate constant k 1 ) (6.7 ( 2.0) × 10 -11 exp{(485 ( 85)/T} cm 3 molecule -1 s -1 was obtained at a pressure of 1 Torr of helium over the temperature range 233-320 K. k 1 was found to be pressure-independent (within 10%) at T ) 298 K in the pressure range 0.25-3 Torr. Both HCl and C 5 H 8 Cl adduct were detected as products of reaction 1. The measurements of the HCl yield as a function of temperature led to the branching fraction for the H-atom abstraction channel (1b): k 1b /k 1 ) (1.22 ( 0.4) exp{-(595 ( 90)/T} (P ) 1 Torr, T ) 233-320 K); k 1b /k 1 ) 0.169 ( 0.022 at 298 K. The results are compared with those reported in a recent study 4 carried out at 298 K. In addition, the rate coefficient has been measured for the reaction Cl + Br 2 f BrCl + Br (2), which was used as the reference in the relative study of reaction 1. Combining the present results obtained in the range 233-320 K with those available from a previous study in the range 298-401 K, 10 the following Arrhenius expression is recommended: k 2 ) (2.3 ( 0.4) × 10 -10 exp{(135 ( 60)/T} cm 3 molecule -1 s -1 .