Electronic Structure and Geometry of Hydrogen Cyanide

Abstract

The geometry and charge distribution of HCN in its ground state has been determined by means of many-electron, self-consistent-field molecular-orbital wavefunctions. LCAO MO SCF calculations and ones which split the AO's with linear variation coefficients yield properties and total energies reasonably close to the molecular Hartree—Fock limit. A linear molecule with bond distances correct to 1% of the microwave spectroscopy values is obtained. Walsh's orbital-energy diagrams are found to be almost independent of angle but with nearly compensating variations and for this molecule Walsh's orbital-energy summation criterion leads to a bent ground state. This result, however, is easily understood in terms of the relatively high ionic character of the H–CN bond. An empirical molecular bind energy correlation scheme based on diatomic molecular Hartree—Fock solutions is employed to analyze the difference between the computed (7.10 eV) and the experimental (13.53 eV) binding energy values.