Characterization of the 1,1-HCl Elimination Reaction of Vibrationally Excited CD sub(3)CHFCl Molecules and Assignment of Threshold Energies for 1,1-HCl and 1,2-DCl plus 1,1-HF and 1,2-DF Elimination Reactions

Vibrationally excited CD sub(3)CHFCl molecules with 96 kcal mol super(-1) of energy were generated by the recombination of CD sub(3) and CHFCl radicals in a room-temperature bath gas. The four competing unimolecular decomposition reactions, namely, 1,1-HCl and 1,2-DCl elimination and 1,1-HF and 1,2-DF elimination, were observed, and the individual rate constants were measured. The product branching fractions are 0.60, 0.27, 0.09, and 0.04 for 1,2-DCl, 1,1-HCl, 1,2-DF, and 1,1-HF elimination, respectively. Electronic structure calculations were used to define models of the four transition states. The statistical rate constants calculated from these models were compared to the experimental rate constants. The assigned threshold energies with plus or minus 2 kcal mol super(-1) uncertainty are 60, 72, 65, and 74 kcal mol super(-1) for the 1,2-DCl, 1,1-HCl, 1,2-DF, and 1,1-HF reactions, respectively. The loose structure of the 1,1-HX transition states, which is exemplified by the order of magnitude larger pre-exponential factor relative to the 1,2-HX elimination reactions, compensates for the high threshold energy; thus, the 1,1-HX elimination reaction rates can compete with the 1,2-HX elimination reactions for high levels of vibrational excitation in CD sub(3)CHFCl. The 1,1-HCl and 1,1-HF reactions are observed via the CD sub(2)=CDF and CD sub(2)=CDCl products formed from isomerization of the CD sub(3)CF and CD sub(3)CCl carbenes. These D-atom migration reactions are discussed, and the possibility of tunneling is evaluated. The transition states developed from the 1,1-HCl and 1,1-HF reactions of CD sub(3)CHFCl are compared to models for the HCl and HF elimination reactions of CHF sub(2)Cl, CHFCl sub(2), and CH sub(2)FCl.