An accurate potential model for the a 3 Σ u + state of the lithium dimer.

An accurate Tang-Toennies (TT) model potential is introduced to describe the interatomic potential of the lithium dimer in the a 3 Σ u + state. With only one well-known parameter, the ionization energy, the new model potential compares favorably with the experimentally fitted Morse/Long-range (MLR) potential of Dattani and Le Roy [ J. Mol. Spectrosc. , 2011, 268 , 199] and is in excellent agreement with the state-of-the-art ab initio potential of Lesiuk et al. [ Phys. Rev. A , 2020, 102 , 062806]. With the known dispersion coefficients and the ionization energy, the new potential requires only two experimental parameters, namely the depth of the potential well D e and its location R e . The new potential can be extended to the region of zero separation by the united atom limit.