Analytical potential energy surface for the GeH_4 + H -> GeH_3 + H_2 reaction: Thermal and vibrational-state selected rate constants and kinetic isotope effects

摘要

The potential energy surface (PES) for the gas-phase GeH_4 + H -> GeH_3 + H_2 reaction and its deuterated analogue (GeD_4+H) was constructed with suitable functional forms to represent the stretching and bending modes, and using as calibration criterion the experimental thermal rate constants and kinetic isotope effects. The thermal rate constants were calculated using variational transition state theory with semiclassical transmission coefficients over the experimental temperature range, 200-500 K. This surface was then used to analyze dynamical features. From the analysis of the reaction path curvature (kappa), we qualitatively find that excitation of the Ge-H stretch in germane enhances the forward reaction rates and the H_2 stretch mode appears vibrationally excited, in accordance with an "early" transition state and an attractive surface. Moreover, as the vibrational modes preserve their characteristic motions (adiabatic behavior) in the forward sense, we quantitatively find that exciting the GeH_4 symmetric stretching mode by one quantum increases the rate constants by a factor of from 5.71 to 3.14 when the temperature increases from 200 to 500 K. Interestingly, this quantitative result validates the qualitative analysis based on the reaction path curvature.