Using two approaches, reaction-path dynamics (which uses information on electronic structure energy and energy derivatives calculated ab initio along the minimum energy path) and dual-level dynamics (in which the reaction-path is calculated at a low level of theory, and stationary point information from a high level of theory is used to interpolate corrections to energy quantities, vibrational frequencies, and moments of inertia), the reaction-path for the CH3F + OH reaction was traced. Qualitatively, both methods yield similar results, showing the usefulness of the more economical dual-level approach. The H2O product may be vibrationally excited due to the nonadiabatic flow of energy between the reaction coordinate and the O-H bound mode. The rate coefficents were calculated for the temperature range 200-1000 K using the variational transition-state theory. The tunneling effect was included in the first approach using the small-curvature tunneling method, and in the second using the microcanonical optimized multidimensional tunneling method. Tunneling plays an important role in this reaction and the calculated rate coefficients show a more pronounced curvature in the Arrhenius plot than the experimental data. © 1998 American Chemical Society.