The proton-coupled proton transfer mechanism, H_2O catalysis, and hydrogen tunneling effects in the reaction of HNCH_2 with HCOOH in the interstellar medium

摘要

The reaction HNCH_2 + HCOOH → H_2NCH _2COOH is supposed to be an important reaction related to the possible origin of amino acids on the early Earth. We find that it has an energy barrier of 87.37 kcal mol~(-1) obtained with MP2/6-311+G** in the gas phase, but it is likely enhanced to occur in the interstellar medium (ISM) through a protoncoupled proton transfer reaction, initiated by HNCH_2 coupled with H_2~+, H_3~+, or H _3~+O. H_2~+, H_2~+, and H_3~+O serve as a donor of energy in the coupled reactions. H~+, which is a key species to the coupled reactions, further, plays a catalytic role in reducing a barrier up to 14.14 kcal mol ~(-1). In the coupled reaction with H_3~+O, H _2O, which can seize, transport, and deliver a proton from HCOOH to H_2NCH_2~+, reduces a barrier up to 14.96 kcal mol~(-1). A significant hydrogen-tunneling pathway is predicted by the temperature dependences of k_H~(CVT/SCT), calculated using the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT). Hydrogen tunneling is another important mechanism to make the reaction happen in the ISM. The achieved results can be applied to discuss the origin of amino acids from the materials of the Earth itself.