MODELS FOR BOND DISTANCE DEPENDENT ALKALI DIMER RARE-GAS POTENTIALS

Analytic expressions for Li2-Rg and Na2-Rg electronic ground state potentials (Rg = He,Ne,Ar,Kr,Xe) that depend on all three Jacobian coordinates, atom-molecule distance R, bond length r, and orientation angle γ, are presented. The potentials are obtained by expanding the repulsive and attractive parts in a two-term Legendre expansion and connecting them via generalized damping functions as proposed by Tang and Toennies [J. Chem. Phys. 80, 3726 (1984) ]. The bond distance dependence (req = 5.051 a.u.≤r≤6.838 a.u. for Li2 and req = 5.809 a.u.≤r≤7.607 a.u. for Na2) is introduced in the repulsive part via the r-dependent shift of the repulsive barrier and in the attractive part via the r dependence of the multipole polarizabilities and effective excitation energies. These potentials are shown to agree reasonably with ab initio data. The resulting values of potential well depth ε and equilibrium distance Rm are used to check the validity of recently proposed direct combining rules for r-dependent potentials. © 1990 American Institute of Physics.