DIRECT DENSITY FUNCTIONAL THEORY DYNAMICS STUDY FOR THE CH3OCF2CF2OCH3 + OH REACTION

The mechanism and kinetics of the reaction of CH3OCF2CF2OCH3 with OH radicals have been studied theoretically by a direct density functional theory dynamics method. All possible H-abstraction channels and displacement processes taking place on two different conformers of CH3OCF2CF2OCH3 have been taken into consideration. The potential energy surface information including the optimized geometries and harmonic vibrational frequencies of all the stationary points and barrier heights involved in these channels were obtained at the BB1K/6-31+G(d,p) level of theory. The rate constants were calculated using improved canonical variational transition state theory (ICVT) with the small-curvature tunneling correction (SCT) over the temperature range of 200-2000 K. The overall rate constant for the title reaction, which was obtained by considering the weight factor of each conformer from the Boltzman distribution function, is in reasonable agreement with the available experimental value. Three-term Arrhenius expression is fitted to be k(T) = 1.56 x 10(-20) T(2.47)exp(-124.64/T) cm(3) molecule(-1) s(-1) (200-2000 K). Also, the enthalpies of formation of the reactant CH3OCF2CF2OCH3 and product radicals CH3OCF2CF2OCH2 and CH3OCF2CF2O, which lack experimental or theoretical data, were evaluated via applying isodesmic reactions.