**7**, 17-23 (1999)

https://doi.org/10.1007/s100530050342

## Electron-pair densities of group 2 atoms in their ^{1}P and ^{3}P terms

^{1}
Department of Applied Chemistry, Muroran Institute of Technology, Muroran,
Hokkaido 050-8585, Japan

^{2}
Institute Carlos I de Física Teórica y Computacional, Facultad de
Ciencias, Universidad de Granada, Granada 18071, Spain

^{3}
Grupo de Modelización y Diseño Molecular, Instituto de Biotecnología,
Universidad de Granada, Granada 18071, Spain

Received:
26
August
1998

Revised:
1
February
1999

Published online: 15 August 1999

Electron-pair intracule (relative motion) and extracule (center-of-mass
motion) densities are studied in both position and momentum spaces for the
and terms of the group 2 atoms Be (atomic number *Z=4*), Mg (*Z=12*), Ca
(*Z=20*), Sr (*Z=38*), Ba (*Z=56*), and Ra (*Z=88*). In position space, 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 naïve
manifestation of the Fermi hole in the triplet. The extracule density in
momentum space shows that the term has a distribution larger in a large
center-of-mass momentum region than the 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

*© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999*