The evaluation of extracule and intracule densities in the first-row hydrides, LiH, BeH, BH, CH, NH, OH and FH, from self-consistent field molecular orbital wavefunctions

Abstract

Extracule (centre of mass) and intracule (relative motion) pair densities are reported for the electronic ground states of the first-row hydrides, LiH, BeH, BH, CH, NH, OH and FH. For each type of two-particle coordinate and for each molecule, the radial, longitudinal and transverse densities are evaluated from self-consistent field molecular orbital wavefunctions constructed from 3-21G Gaussian basis sets. The radial intracule density I(r), the longitudinal intracule density L(i)(z) and the longitudinal extracule density L(e)(Z) evolve systematically from double maxima functions in LiH to single maximum functions in FH, whereas the extracule radial density E(R), the transverse extracule density T(i)(b) and the transverse extracule density T(e) (B) exhibit a single maximum in every case. These observations are explained in terms of the ionic character of the bond, the number of electron pairs, the probable orientations of the interelectronic vectors and the orientation of the vectors describing the centre of mass of an electron pair.