Kinetics and thermochemistry of the methyl radical: Study of the CH₃ + HCl reaction

Abstract

Abstract The kinetics of the reaction between CH 3 and HCl was studied in a tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature (296–495 K) and were fitted to an Arrhenius expression: k 1 = 5.0(±0.7) × 10 −13 exp{−1.4(±0.3) kcal mol −1 / RT } cm 3 molecule −1 s −1 . This information was combined with known kinetic parameters of the reverse reaction to obtain Second Law determinations of the methyl radical heat of formation {34.7(±0.6) kcal mol −1 } and entropy {46(±2) cal mol −1 K −1 } at 298 K. Using the known entropy of CH 3 , a more accurate Third Law determination of the CH 3 heat of formation at this temperature was also obtained {34.8(±0.3) kcal mol −1 }. The values of k 1 obtained in this study are between those reported in prior investigations. The results were also used to test the accuracy of the thermochemical information which can be obtained from kinetic studies of R + HX (X = Cl, Br, I) reactions of the type described here.