Ab initio theoretical study of dipole-bound anions of molecular complexes. [H2O⋯HCN]− and [HCN⋯H2O]− anions

Ab initio calculations have been performed to determine structures and adiabatic electron affinities of water complexes of hydrogen cyanide. In these systems the excess electron is bound by the dipole field of the complex. Based on the calculations we determined that, as for the neutral complexes, there are two equilibrium anion structures, [HCN⋯H2O]− and [H2O⋯HCN]−. Upon electron attachment to the neutral H2O⋯HCN complex, which the only system detected in the gas phase, its stability with respect to the HCN⋯H2O complex increases even further, from 1.4 kcal/mol to 3.0 kcal/mol. The adiabatic electron affinities of H2O⋯HCN and HCN⋯H2O complexes are predicted to be 86 and 17 meV, respectively.