Applications of a simple molecular wavefunction. Part 6.—FSGO open-shell calculations on first-row diatomic molecular systems

Abstract

Calculations are presented on a series of diatomic systems, made using the FSGO basis. In general, the prediction of internuclear distances is good. The dissociation energy of Li+2, which has a one-electron bond, is accurately calculated, but mostly dissociation cannot be reproduced properly by the model. The lithium molecule is predicted to have a small electron affinity (ca. 0.3 eV), and the resultant Li–2 ion is further predicted to have an anomalous 2Πu ground state. The isoelectronic LiBe system is forecasted to be bound also in a 2Π configuration with a bond strength of 44 kJ/mol. Be+2, however, is found to have the anticipated 2∑+u ground state configuration. Ground (X2∑+) and first excited state (A2Π) calculations have been made for BeH and BH+, and the trends in several properties are correctly followed; in particular, the trend in the A→X transition and the directions in which the bond lengths change between ground and first excited states. BH– is predicted to exist in a 1 σ2 2σ2 1π2 3σ configuration, probably with a 4∑– ground state. The detailed results for CH are discussed in terms of changes in the orbital exponents between atomic and molecular systems. Finally, calculations of several first ionisation potentials are presented and discussed.