Department of Chemistry, University of Toronto, Toronto, Canada MSS 1A1
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 CH3Cl to CH3Br to CH3I, 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 CH2Cl, CHCl2, CCl3, due to increase in the number of secondary encounters between HF and the departing radical.