Energy distribution among reaction products. XIV. F + CH 4, F + CH 3X(X  Cl, Br, I), F + CH nCl 4− n( n = 1−3)

Abstract

The infrared chemiluminescence technique has been used to obtain relative rate constants k(ν′) for HF(ν′) formed in the following reaction: ▪ For reaction (1) the detailed rate constants [ k(ν′ = 1) = 0.30; k(ν′ = 2) = 1.00; k(ν′ = 3) = 0.15; mean fraction of the available energy entering vibration <⨍ ′ ν> = 0.56] confirmed, at much lower reagent pressures, results obtained by previous workers. In series I there was a slight increase in fraction of the energy entering vibration as the molecular reagent altered from CH 3Cl to CH 3Br to CH 3I, viz <⨍ ′ ν> = 0.50 (1a), <⨍ ′ ν> = 0.58 (1b), <⨍ ′ ν> = 0.60 (1c). In series 2, by contrast, there was a marked decrease in fractional conversion of the available energy into vibration with increasing chlorination of the molecular reagent; <⨍ ′ ν> = 0.50 (1a), <⨍ ′ ν> = 0.23 (2a), <⨍ ′ ν> = 0.13 (2b). The rate constants into ν′ = 0, k(ν′ = 0), were obtained by extrapolation of surprisal plots; the trends for both series were, however, also evident from k(ν′ > 0). No separate initial rotational distribution was observed for any of these reactions, indicating that the peak of the initial distribution is not far removed from a 300 K thermal distribution. The decrease in <⨍ ′ ν> for the HF products along series 2 was tentatively ascribed to increasing internal excitation in the ejected radicals CH 2Cl, CHCl 2, CCl 3, due to increase in the number of secondary encounters between HF and the departing radical.