Electron - pair densities of group 2 atoms in their 1 P and 3 P terms

Electron-pair intracule (relative motion) and extracule (center-of-mass motion) densities are studied in both position and momentum spaces for the difference in the intracule densities shows that the probability of a small interelectronic distance is larger in the triplet for all the six atoms, as reported for the lightest Be atom in the literature. The position-space extracule density clarifies that the triplet electrons are more likely to be at opposite positions with respect to the nucleus than the singlet electrons for all the atoms. In momentum space, the singlet generally has a larger probability of a small relative momentum between two electrons as a na¨ıve manifestation of the Fermi hole in the triplet. The extracule density in momentum space shows that the 1 P term has a distribution larger in a large center-of-mass momentum region than the 3 P term. PACS. 32.10.+z Theory of electronic structure, electronic transitions, and chemical binding – 31.15.-p Calculations and mathematical techniques in atomic and molecular physics