Dissociative recombination of HCNH+: Absolute cross-sections and branchingratios

The dissociative recombination (DR) of HCNH+ has been studied at the heavy ion storage ring CRYRING. The absolute cross-sections have been measured be tween 0.01 meV and 0.2 eV collision energy. The DR thermal rate coefficient s, which can be directly applied to modeling environments in thermal equili brium, have been found to be 2.8 x 10(-7)(300/T)(0.65) at temperatures T < 1000 K. The DR branching fractions have been measured for different dissoci ation channels: HCN(HNC)+H (0.67), CN + H-2 (0.0), and CN+H+H (0.33) at col lision energy of 0 eV. The results show that DR of HCNH+ is an efficient pr ocess leading to formation of HCN or HNC isomers, whereas CN production is dominated by three-body fragmentation. The multireference self-consistent c alculations in a complete active space have been used as a common backgroun d for all studied species and reaction paths. Three-body fragmentation CN+H +H has been considered in one concerted elementary reaction step.