Theoretical studies of the thermal and chemically activated decomposition of CF3CY2O (Y = F, H) radicals

The C-C bond scission of three fluorinated ethoxy radicals CF3CF2O, CF3CFHO and CF3CH2O has been investigated using current theoretical methods. Quant um chemical calculations were performed to derive structures and vibrationa l frequencies at the B3LYP/cc-pVTZ(+ 1) level. Higher level ab initio data such as critical energy barriers are provided by application of a modified G3(MP2)-theory. The results have been used as input to statistical kinetic calculations. Complete fall-off curves for the thermal decomposition of all three radicals were calculated in a weak collision treatment by use of RRK M theory and subsequent solution of the master equation. As a part of our c alculations rate coefficients of k(dec) = 1.1 x 10(4) s(-1), 5.3 x 10(6) s( -1) and 7.4 x 10(-5) s(-1) for the thermal decomposition of CF3CFHO, CF3CF2 O and CF3CH2O radicals by C-C fission, respectively, at atmospheric pressur e and a temperature of 300 K were obtained. From a comparison with previous experimental studies on the ratio k(dec)/ko(2) for the CF3CFHO radical we recommend a rate coefficient of ko(2) = 4.2 x 10(-16) cm(3) molecule(-1) s( -1) for the reaction of CF3CFHO with O-2 at 300 K. In addition, a simple ap proach is developed to calculate the time-dependent decomposition rate coef ficient of vibrationally excited CF3CFHO radicals as they might originate t hrough chemical activation from the exothermic reaction of CF3CFHOO with NO . It is concluded, that the inclusion of vibrational chemical excitation of CF3CFHO radicals results in prompt decomposition yields likely to be large r than 35%.