Theoretical Elucidation of the Unusually High [HNC]/[HCN] Abundance Ratio in Interstellar Space: Two‐dimensional and Two‐State Quantum Wave Packet Dynamics Study on the Branching Ratio of the Dissociative Recombination Reaction HCNH++e−→ HNC/HCN + H

In order to elucidate the unusually high [HNC]/[HCN] abundance ratio observed in interstellar space, we have carried out wave packet simulations for the dissociative recombination reaction HCNH + + e - → HNC/HCN + H on the two-dimensional potential energy surfaces (PESs) of two dissociative electronic states of HCNH, 1 2 Σ + and 2 2 Σ + . Two adiabatic PESs of 1 2 Σ + and 2 2 Σ + have been determined as functions of NH and CH bond lengths for a linear geometry of HCNH with a fixed CN bond length, by the multireference single and double configuration interaction plus Davidson's quadruple excitation correction [MR-SDCI(+Q)] method. The wave packets, generated from the low-lying vibrational eigenstates of HCNH + , have been put initially on the 2 2 Σ + adiabatic PES. The resulting branching ratios of [HNC]/[HCN] vary from 0.77 to 1.32, depending on the initial vibrational quantum numbers, which support that HCNH + is the precursor of both HNC and HCN in interstellar space.