A possible role for triplet H2CN/+/ isomers in the formation of HCN and HNC in interstellar clouds

The structures and energies of the lowest triplet states of four isomers of H2CN(+) have been determined by self-consistent field and configuration interaction calculations. When both hydrogen atoms are attached to the nitrogen atom, H2NC(+), the molecule has its lowest triplet state energy, which is 97.2 kcal/mol above the energy of the linear singlet ground state. The structure has C2v symmetry, with an HCH bond angle of 116.8 deg, and bond lengths of 1.009 A (H-N) and 1.268 A (N-C). It is suggested that the triplet H2NC(+) isomer may play a role in determining the relative yields of HCN and HNC from the reaction of C(+) and NH3. Specifically, a triplet path is postulated in which C(+) and NH3 yield the triplet H2NC(+) isomer, which then yields the singlet H2NC(+) isomer by phosphorescent emission. Because this emission removes a large amount of energy, the singlet H2NC(+) isomer may have insufficient energy to isomerize to the linear singlet ground state. Subsequent dissociative recombination would yield the HNC isomer exclusively.