ELSEVIER ChemicalPhysics 219 (1997) 161-172
Inclusion of ion-pair states in the diatomics-in-molecules
description of potential energy surfaces: van der Waals complexes
of He-C12 and Ar-C12
B.L. Grigorenko a, A.V. Nemukhin a, V.A. Apkarian b,*
a Department of Chemistry, Moscow State University, Moscow 119899. Russian Federation
b Department of Chemistry, University of California, Irvine, CA 926192-2025, USA
Received 14January 1997
It is shown that the inclusion of excited ionic configurations in the diatomics-in-molecules(DIM) Hamiltonian serves as a
natural means to account for main features of non-additivity in three-body potential energy surfaces of He-CI 2 and Ar-CI 2
van der Waals complexes. For ground state C12(1Eg), while consideration of only neutral configurations leads to T-shaped
isomers, inclusion of the excited CI+C1 - configuration stabilizes the linear isomer and destabilizes the T-shaped isomer.
Within the same formalism, the excited C12(3I]) only sustains minima in the T-shaped isomer. Potential energy surfaces
created with a minimal DIM basis are constructed and shown to compare favorably with the most accurate ab initio surfaces
and experiments. Analytical forms are given for the three-body surfaces, meant for fitting purposes and as a convenience in
simulations of dynamics. © 1997 Elsevier Science B.V.