Dual level reaction-path dynamics calculations on the C{sub 2}H{sub 6} + OH {r_arrow} C{sub 2}H{sub 5} + H{sub 2}O reaction

Interpolated Variational Transition State Theory with Multidimensional Tunneling contributions (IVTST/MT) has been applied to the reaction of C{sub 2}H{sub 6} + OH, and it yields rate constants that agree well with the available experimental information. The main disadvantage of this method is the difficulty of interpolating all required information from a few points along the reaction path. A more recent alternative is Variational Transition State Theory with Multidimensional Tunneling and Interpolated Corrections (VTST/MT-IC, also called dual-level direct dynamics), in which the reaction-path properties are first determined at an economical (lower) level of theory and then {open_quotes}corrected{close_quotes} using more accurate information obtained at a higher level for a selected number of points on the reaction path. The VTST/MT-IC method also allows for interpolation through die wider reaction swath when large-curvature tunneling occurs. In the present work we examine the affordability/accuracy tradeoff for several combinations of higher and lower levels for VTST/MT-IC reaction rate calculations on the C{sub 2}H{sub 6} + OH process. Various levels of theory (including NDDO-SRP and ab initio ROMP2, UQCISD, UQCISD(T), and UCCSD) have been employed for the electronic structure calculations. We also compare several semiclassical approaches implemented in the POLYRATE and MORATE programs for taking tunneling effectsmore » into account.« less