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

摘要

Electron-pair intracule (relative motion) h(u) and extracule (center-of-mass motion) d(r) densities are studied for the ~3P, ~1D, and ~1S multiplet states of five group 14 atoms with p~2 configurations, the ~4S, ~2D, and ~2P multiplets of five group 15 atoms with p~3 configurations, and the ~3P, ~1D, and ~1S 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 angular momentum state is always accompanied with the decrease of the electron-nucleus attraction energy V_(en) which is greater than the increase in the electron-electron repulsion energy V_(ee), as discussed in the literature for a few light atoms. In all the cases, the difference in the radial intracule densities 4#pi#u~2h(u) clarifies that for a multiplet with a higher angular momentum, the probability of finding a pair of electrons separated by a short/long distance is larger/smaller, leading to a greater V_(ee) and a smaller average interelectronic distance . The Fermi hole effect is not important for the relative stability of the multiplets examined. For the multiplets arising from the p~n electronic configurations, the differences in the radial extracule densities 4#pi#RE~2d(R) are found to be almost isomorphic with the corresponding intracule ones: In a multiplet with a high angular momentum, the average center-of-mass radius of an electron pair is always smaller, and two electrons are more likely to be at opposite positions with respect to the nucleus. Accordingly, the valence p orbital in a more stable multiplet is more tight, resulting in a lower electron-nucleus attraction energy V_(en) for all the 15 atoms.