Contribution of the core-excited ²Φ state to direct dissociative recombination of HCO

New quantum-chemical calculations for both spatial symmetries (A' and A″) of the second-lowest core-excited doublet state ²Φ of HCO are presented, including coupling matrix elements to the initial electronic continuum state HCO⁺ + e^- at collision energy ε. Using three-dimensional grid-based wave packet propagation, the contribution of the ²Φ state to the dissociative-recombination cross section of HCO⁺ is computed. It is found that the H + CO(a') channel is dominant and that inclusion of the ²Φ state substantially improves the agreement between theory and experiment for ε ≥ 1 eV.