SCF-CI studies on the electronic ground state of water: Potential energy hypersurface and spectroscopic constants

Abstract

Large-scale Hartree-Fock self-consistent field calculations, employing extended Gaussian basis sets, and configuration interaction studies are performed to calculate the energy hypersurface of the electronic ground state of the water molecule and to investigate the accuracy requirements in view of the determination of molecular spectroscopic constants. From the calculated points on the hypersurface the theoretical equilibrium geometry, the force field through fourth order, the spectroscopic constants ω_i, x_ij, α_i as well as the Darling-Dennison and Fermi resonance constants are evaluated. The CI surface yields an equilibrium structure for H₂O withr _e = 0.9501 Å and α_e=105.33 ° (r _exp = 0.9572 Å and α_exp = 104.52 °). The vibrational levels are obtained with a systematic error of about 2 percent and the rotational constants to about 1 percent compared to spectroscopic data. The relative energy maximum corresponding to the linear structure with α = π is calculated to be 11890cm⁻¹, within the error limits of the values deduced from experimental measurements.