Reaction mechanism of the astrochemical electron capture reaction HCNH++e-→HNC+H:: a direct ab initio dynamics study

Electron capture processes of HCNH+, HCNH++e(-)--> HNC+H, have been studied by means of direct ab-initio dynamics calculations in order to elucidate the reaction mechanism. The dynamics calculation of the HCNH+ ion at 10 K showed that the structure of HCNH+ is slightly deformed by thermal activation, while the bond angles in HCNH+ are fluctuated around its equilibrium point. In the dynamics calculations of HCNH, we assumed that auto-ionization does not take place, once the HCNH+ ion captures an electron. The dynamics calculations of HCNH following vertical electron capture of the HCNH+ ion showed that two channels contribute to the reaction. One is a dissociation channel in which the hydrogen in the N-H bond is dissociated via a short-lived complex HCNH. The other channel is the complex formation in which a long-lived complex HCNH is formed after the electron capture. It was found that branching of the channels is dominated by the initial structure of HCNH+ before the electron capture: the electron capture of HCNH+ with larger bending angles leads to complex formation, whereas a trajectory from the structure close to the collinear skeleton leads to the direct dissociation channel. The reaction mechanism of the electron capture processes of HCNH+ is discussed on the basis of these theoretical results.