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The recombination of CF2Cl and CH2F radicals was used to prepare CF2ClCH2F* molecules with 93 ± 2 kcal mol−1of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF2CHF, (2) isomerization to CF3CH2Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFClCHF. Since the isomerization reaction is 12 kcal mol−1exothermic, the CF3CH2Cl* molecules have 105 kcal mol−1of internal energy and they can eliminate HF to give CF2CHCl, decompose by rupture of the C−Cl bond, or isomerize back to CF2ClCH2F. These data, which provide experimental rate constants, are combined with previously published results for chemically activated CF3CH2Cl* formed by the recombination of CF3and CH2Cl radicals to provide a comprehensive view of the CF3CH2Cl* ↔CF2ClCH2F* unimolecular reaction system. The experimental rate constants are matched to calculated statistical rate constants to assign threshold energies for the observed reactions. The models for the molecules and transition states needed for the rate constant calculations were obtained from electronic structures calculated from density functional theory. The previously proposed explanation for the formation of CF2CHF in thermal and infrared multiphoton excitation studies of CF3CH2Cl, which was 2,2-HCl elimination from CF3CH2Cl followed by migration of the F atom in CF3CH, should be replaced by the Cl/F interchange reaction followed by a conventional 1,2-ClH elimination from CF2ClCH2F. The unimolecular reactions are augmented by free-radical chemistry initiated by reactions of Cl and F atoms in the thermal decomposition of CF3CH2Cl and CF2ClCH2F. [ABSTRACT FROM AUTHOR]

Vibrationally excited CF2BrCF2CH3and CF2BrCF2CD3molecules were prepared with 96 kcal mol-1energy at room temperature by the recombination of CF2BrCF2and CH3(CD3) radicals. The observed unimolecular reactions are 1,2-BrF interchange to give CF3CFBrCH3(CD3) molecules and 2,3-FH (FD) elimination; the rate constants are 2.2 × 105(1.5 × 105) s-1and 2.0 × 105(0.75 × 105) s-1, respectively. The CF3CFBrCH3(CD3) molecules rapidly, relative to the reverse reaction, eliminate HBr or DBr to give the observed product CF3CFCH2(CD2). Density functional theory at the B3PW91/6-311G(2d,p) level was used to obtain vibrational frequencies and moments of inertia of the molecule and transition states for subsequent calculations of statistical rate constants for CF2BrCF2CH3and CF2BrCF2CD3. Matching experimental and calculated rate constants gave threshold energies of 62 and 66 kcal mol-1for 1,2-BrF interchange and 2,3-FH elimination, respectively. The BrF interchange reaction is compared to ClF interchange from CF2ClCF2CH3and CF2ClCHFCH3. [ABSTRACT FROM AUTHOR]