Electronic Structure of N2, CO, and BF

Abstract

Approximate Hartree—Fock calculations are reported for the 1Σ+ ground states of the isoelectronic 14-electron molecules N2, CO, and BF. In each case calculations have been carried out at five internuclear distances, chosen as the roots of an appropriately scaled Chebyshev polynomial, in order to facilitate interpolation. Electronic kinetic and potential energies, mean values of 1/r about each nucleus, and mean values of z, 3z2—r2, and r2 are obtained at each internuclear distance. The production runs used basis sets consisting of two exponential functions for each occupied atomic orbital plus dσ and dπ orbitals on each atom, combined to form molecular orbitals by the matrix Hartree—Fock (SCF—LCAO) method. It was found that 4fσ and 4fπ orbitals, with optimized exponents, contribute 0.3 eV to the dissociation energy of N2, but these orbitals were not included in the production runs. The effect on CO and BF of 4f orbitals is expected to be somewhat smaller. Various spectroscopic quantities (re, ωe, xeωe, Be) and electric dipole and quadrupole moments are computed and are in general qualitative agreement with experimental values. The polarity of the dipole moment of CO, while not definitely determined by present calculations, is indicated to be C+O—. The experimental determination of this polarity is discussed critically, and it is concluded that a definitive determination of the sign is not possible from microwave data, which had previously been interpreted to imply the polarity C—O+. Thus an independent redetermination of this sign is required. Dissociation energies are discussed in connection with an empirical estimate of the net correlation energy contribution to molecular binding.