2006ApJ...636..927I

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 ²Σ⁺ and 2 ²Σ⁺. Two adiabatic PESs of 1 ²Σ⁺ and 2 ²Σ⁺ 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 ²Σ⁺ 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.