Theoretical Study of the Kinetics of F-atom Abstraction Reactions from F2, CF2(OF)2, CF3OF and SF5OF by CO

The kinetics of the fluorine atom abstraction reactions RF+CO -> R+FCO (with R=F, CF2(OF)O, CF3O, and SF5O) has been theoretically studied using the density functional theory and ab initio composite models. The derived average activation energies for the reactions of CO with F-2 and with CF2(OF)(2) of 15.4 kcal mol(-1), at 290-320 K, and 23.1 kcal mol(-1), at 386-420 K, are in good agreement with the experimental ones. For the F-atom abstraction from the CF3OF and SF5OF molecules, values of 22.7 and 22.5 kcal mol(-1) were calculated. Over the 290-320 and 386-420 K temperature ranges, preexponential factors of 1.1 x 10(-12) and 4.4 x 10(-12) cm(3) molecule(-1) s(-1) were respectively determined for the reactions of CO with F-2 and CF2(OF)(2) which are 60% larger than the experimental. Values of 2.3 x 10(-12) and 1.2 x 10(-12) cm(3) molecule(-1) s(-1) were obtained for the reactions corresponding to the SF5OF and CF3OF molecules at 353-383 and 383-423 K, respectively. Unexpectedly, the omega B97X-D, M06-2X and BMK functionals lead to energy barriers much higher than those predicted by other quantum-chemical models.