Ab initio mechanism and thermal rate constants for the reaction of atomic H with Ge2H6

Abstract

The reaction of digermane Ge₂H₆ with atomic H has been studied theoretically. The detailed mechanism has been revealed for the first time. This reaction involves not only abstraction but also substitution. The calculation shows that there are two transition states for the substitution reaction: (1) frontside attack of the Ge–Ge bond by the hydrogen atom and (2) backside attack of the GeH₃ group by the hydrogen atom along the Ge–Ge axis, forming a transition state structure with C_3v symmetry. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction path for each channel are discussed and compared. On the basis of the ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory (CVT) with the small-curvature tunneling (SCT) correction method over the temperature range of 200–3000 K. The theoretical results have been compared with available experimental data. The kinetics calculations show that the variational effect is small for all the channels and in the lower temperature range, the small-curvature tunneling effect is important for the abstraction channel and the substitution channel with backside attack. At lower temperatures, the major product channel is direct hydrogen abstraction leading to Ge₂H₅ and H₂, whereas the substitution reaction with frontside attack becomes the dominant channel at higher temperatures. The substitution reaction with backside attack is a minor channel over the whole studied temperature range.