State of the art for ab initio vs empirical potentials for predicting 6e$^{-}$ excited state molecular energies: Application to Li$_{2}\left(b,1^{3}Π_{u}\right)$

Abstract

We build the first analytic empirical potential for the most deeply bound Li2 state: b 1 3 Πu . Our potential is based on experimental energy transitions covering v = 0 − 34, and very high precision theoretical long-range constants. It provides high accuracy predictions up to v = 100 which pave the way for high-precision long-range measurements, and hopefully an eventual resolution of the age old discrepancy between experiment and theory for the Li 2 2 S + Li 2 2 P C3 value. State of the art ab initio calculations predict vibrational energy spacings that are all in at most 0.8 cm −1 disagreement with the empirical potential.