Tatiana Korona^{a}, Bogumil Jeziorski^{a}, Robert Moszynski^{a},
and Geerd H.F. Diercksen^{b}

^{a} Department of Chemistry, University of Warsaw, Pasteura
1, 02-093 Warsaw, Poland
^{b} Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse
1, D-85740 Garching, Germany

*Degenerate Symmetry-Adapted Perturbation Theory of
Weak Interactions between Closed- and Open-Shell Monomers. Application
to Rydberg States of Helium Hydride*

**Abstract**

Symmetry-adapted perturbation theory is extended to the (quasi)degenerate,
open-shell case. The new formalism is tested in the calculations of the
interaction energies for a helium atom in the ground state interacting
with an excited hydrogen atom. It is shown that the method gives satisfactory
results in low orders if the coupling with higher Rydberg states of the
dimer is small, as it is the case for the A^{2}^{+},
B^{2},
E^{2},
3^{2}, and
1^{2}
states of HeH. For the C^{2}^{+} state the convergence
of the method is very slow, but it can be improved by including the *n*=3
states into the model space.

Back to the publication list of Tatiana KoronaTatiana Korona 2003-01-16