Electron-pair densities of group 14, 15, and 16 atoms in their low-lying multiplet states

Electron-pair intracule (relative motion) h(u) and extracule (center-of-mas s motion) d(R) densities are studied for the P-3, D-1, and S-1 multiplet st ates of five group 14 atoms with p(2) configurations, the S-4, D-2, and P-2 multiplets of five group 15 atoms with p(3) configurations, and the P-3, D -1, and S-1 multiplets of five group 16 atoms with p(4) configurations. For all 15 atoms, it is confirmed that a lower total energy E in a high angula r momentum state is always accompanied with the decrease of the electron-nu cleus attraction energy V-en which is greater than the increase in the elec tron-electron repulsion energy V-ee, as discussed in the literature for a f ew light atoms. In all the cases, the difference in the radial intracule de nsities 4 pi u(2)h(u) clarifies that for a multiplet with a higher angular momentum, the probability of finding a pair of electrons separated by a sho rt/long distance is larger/smaller, leading to a greater V-ee and a smaller average interelectronic distance [u]. The Fermi hole effect is not importa nt for the relative stability of the multiplets examined. For the multiplet s arising from the p(n) electronic configurations, the differences in the r adial extracule densities 4 pi R-2 d(R) are found to be almost isomorphic w ith the corresponding intracule ones: In a multiplet with a high angular mo mentum, the average center-of-mass radius [R] of an electron pair is always smaller, and two electrons are more likely to be at opposite positions wit h respect to the nucleus. Accordingly, the valence p orbital in a more stab le multiplet is more tight, resulting in a lower electron-nucleus attractio n energy V-en for all the 15 atoms. (C) 1999 American Institute of Physics. [S0021-9606(99)30312-3].