Effects of multidimensional tunneling in the kinetics of hydrogen abstraction reactions of O (3 P) with CH3 OCHO.

Quantum tunneling paths are important in reactions when there is a significant component of hydrogenic motion along the potential energy surface. In this study, variational transition state with multidimensional tunneling corrections are employed in the calculations of the thermal rate constants for hydrogen abstraction from the cis-CH3 OCHO by O (3 P) giving CH3 OCO + OH (R1) and CH2 OCHO + OH (R2). The structures and electronic energies are computed with the M06-2X method. Benchmark calculations with the CBSD-T approach give an enthalpy of reaction at 0 K for R1 (-2.8 kcal/mol) and R2 (-2.5 kcal/mol) which are in good agreement with the experiment, i.e. -2.61 and -1.81 kcal/mol. At the low and intermediate values of temperatures, small- and large-curvature tunneling dominate the kinetics of R1, which is the dominant path over the range of temperature from 250 to 1200 K. This study shows the importance of multidimensional tunneling corrections for both R1 and R2, for which the total rate constant at 298 K calculated with the CVT/µOMT method is 8.2 × 10-15 cm3 molecule-1 s-1 which agrees well with experiment value of 9.3 × 10-15 cm3 molecule-1 s-1 (Mori, Bull. Inst. Chem. Res. 1981, 59, 116). © 2018 Wiley Periodicals, Inc.