Ab initio electronic structure of HCN- and HNC- dipole-bound anions and a description of electron loss upon tautomerization

The binding of an excess electron to HCN and HNC was studied at the coupled cluster level of theory with single, double, and noniterative triple excit ations and with extended basis sets to accommodate the loosely bound excess electron. The HCN molecule, with a dipole moment of 3.05 Debye, binds an e lectron by 10 cm(-1), whereas the HNC tautomer possesses a similar dipole m oment (3.08 Debye) and binds the electron by 43 cm(-1). The electronic stab ility of the anionic system along the minimum energy HCN --> HNC tautomeriz ation path has been investigated, and it was concluded that the excess elec tron autodetaches during the tautomerization. Unusually large electron corr elation energy contributions to the total electron binding energy were foun d and are discussed. (C) 2001 American Institute of Physics.