Effective core potentials and accurate energy curves for Cs2 and other alkali diatomics

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Abstract
Energy curves of Cs2 that correlate to the ground (SS) and first excited asymptote (SP) are calculated using compact effective potentials (CEP) and core polarization potentials (CPP) which reduce the alkali atom to a single valence electron. Dissociation energies and equilibrium internuclear separations are in good agreement with experimental values. The long‐range properties of the energy curves are analyzed to determine the region where the chemical interactions begin. Analogous energy curves and spectroscopic constants are obtained for the Rb2 molecule. The ground state singlet and triplet energy curves are also determined for K2. For completeness, the ground state spectroscopic constants are also reported for the Li and Na neutral and cation homonuclear diatomic molecules to illustrate the accuracy of the CEP and CPP for all the alkali atoms. Both doublet and quartet energy curves of the homonuclear anions also were examined. The dissociation energies and electron detachment energies of the doublet ground state for Rb−2 and Cs−2 are in good agreement with experiment. An assignment of the photoelectron spectra of Cs−2 is possible from the electronic structure of the ground state and the excitation energies of the neutral states. Quartet excited states of Cs−2 are calculated to be bound relative to the 3Σ+u neutral state but are metastable with respect to the ground 1Σ+g state. The accuracy of the ionic energy curves shows that the CEP and CPP are transferrable to the ionic systems.