Kinetics of the recombination reactions of CClF with CF2 and with CClF

The laser flash photolysis-absorption technique has been used to study the CClF + CF2 + M --> C2ClF3 + M and CClF + CClF + M --> C2Cl2F2 + M recombina tion reactions at 297 K. Both reactions were found to be essentially at the second-order regime from 10 Torr of the CClF and CF2 radicals precursor C2 ClF3 up to 750 Torr of mixtures of C2ClF3/He. The derived limiting high-pre ssure rate coefficients are (9 +/- 2) x 10(-13) and (1.2 +/- 0.2) x 10(-12) cm(3) molecule(-1) s(-1), respectively. An analysis in terms of the ab ini tio density functional theory and the statistical adiabatic channel model ( SACM) indicates that the formation of chlorine atoms by unimolecular decomp osition of the initially formed C2ClF3 or C2Cl2F2 energized adducts can be discarded at room temperature. Employing isodesmic reaction schemes at the B3LYP/6-311+ + G(d,p) level of theory, the enthalpy of formation of C2Cl2F2 , C2ClF2 and C2F3 are calculated to be -78.3 +/- 4, - 18.1 +/- 4 and - 59.9 +/- 4 kcal mol(-1), respectively. (C) 1999 Elsevier Science B.V. All right s reserved.