Dual-level direct dynamics studies for the reactions of CH3OCH3 and CF3OCH3 with the OH radical

The reactions of CH3OCH3+OH (R1) and CF3OCH3+OH (R2) via two hydrogen abstraction channels are investigated theoretically using the dual-level direct dynamics approach. The minimum energy path calculation is carried out at the MP2/6-311G(d,p) level, and energetic information is further refined by the G3 theory. For each reaction hydrogen abstraction is favored for the out-of-plane hydrogen, while the abstraction from the in-plane hydrogen is a minor channel. Hydrogen-bonded complexes are present on the reactants and products sides of the primary channel, indicating that the reactions may proceed via an indirect mechanism. By means of variational transition state theory with interpolated single-point energies method the dynamic results of all channels are obtained, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants are in good agreement with the experimental data and are fitted to be k(1)=3.33x10(-20) T-2.91 exp(-409.7/T) and k(2)=1.23x10(-24) T(3.93)exp(-188.2/T) cm(3) molecule(-1) s(-1) over the temperature range 230-2000 K. The calculation indicates the CH3OCH3+OH reaction may proceed much easier than the CF3OCH3+OH reaction and fluorine substitution decreases the reactivity of the C-H bond. (C) 2003 American Institute of Physics.