Abstract
The kinetics of CF 3 CFHO radical reactions was studied at 20 and 35 Torr and from 259 to 297 K by flash photolysis with time-resolved mass spectrometry. The CF 3 CFHO 2 radical was generated by flash photolysis of Cl 2 in the presence of CF 3 CFH 2 and O 2 , and CF 3 CFHO was formed by the reaction of CF 3 CFHO 2 with Cl and by the peroxy radical self-reaction. The rate coefficient ratio for (1) CF 3 CFHO + O 2 → CF 3 C(O)F + HO 2 and (2) CF 3 CFHO → HC(O)F + CF 3 was determined by observing the formation of HC(O)F as a function of the partial pressure of O 2 . At 20 Torr, k 1 /k 2 = (2.4 ′ 0.8) × 10 - 2 5 e ( 4 2 4 8 ′ 5 5 0 ) / T cm 3 molecule - 1 , and at 35 Torr, k 1 /k 2 = (9.1 ′ 3.3) x 10 - 2 6 e ( 4 3 7 0 ′ 5 0 0 ) / T cm 3 molecule - 1 . Ab initio molecular orbital calculations for optimized geometries, vibrational frequencies, and total energies of CF 3 CFHO, the reaction products, and the C-C bond-breaking transition state were made. Energies were calculated by the G2 and G2(MP2) methods. An RRKM model for reaction 2 was based on geometries and energies from the ab initio calculations. RRKM calculated values of k 2 were combined with the experimentally determined k 1 /k 2 to estimate k 1 . Comparisons were made with estimates made with two other RRKM models (Schneider, W. F.; Wallington, T. J.; Barker, J. R.; Stahlberg, E. A. Ber. Bunsen-Ges. Phys. Chem. 1998, 102, 1850; Somnitz, H.; Zellner, R. Phys. Chem. Chem. Phys. 2001, 3, 2352). The ab initio calculations predict the 298 K enthalpy of formation of CF 3 CFHO to be -203.0 kcal mol - 1 (G2MP2) and -203.4 kcal mol - 1 (G2).
Published Version
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