Theoretical modeling of the hydrogen abstraction reaction of fluoromethaneby the hydroxyl radical

We have performed theoretical modeling of the reaction rate constants of th e hydrogen abstraction reaction of fluoromethane (CH3F) by the hydroxyl rad ical (OH) using dual-level variational transition state theory calculation including multidimensional tunneling corrections from 200 to 1000 K. Correl ated electronic structure theory with extended basis set calculation was ap plied for both the low-level reaction-path and the high-level stationary-po int calculation. An improved interpolated correction scheme was used for be tter estimating the width of energy barrier by performing an intermediate-l evel electronic structure calculation. The calculated rate constants are in good agreement with available experimental values at most temperatures. Th e hydrogen kinetic isotope effects (KIEs) were also evaluated and analyzed. The current study suggested that the reaction has a relatively wide barrie r, and the tunneling effects are thus not very important even at low temper atures. The current study also showed that the variational effects, which l owered the rate constants by over an order of magnitude at room temperature , are very important for the reaction. The best estimate of the classical b arrier height is between 2.8 and 3.1 kcal/mol. The calculation also suggest ed that the calculated KIEs are sensitive to the theories employed for obta ining the low-level potential energy surfaces. It is demonstrated that the dynamical behaviors predicted by the current calculation can also be deduce d from future KIE experiments on the current reaction.