Binding energies of the ground triplet state a3Σu+ of Rb2 and Cs2 in terms of the generalized Le Roy-Bernstein near-dissociation expansion

Formulae of Le Roy-Bernstein near-dissociation theory are derived in a general isotope-invariant form, applicable to any term in the rotational expansion of a diatomic ro-vibrational term value. It is proposed to use the generalized Le Roy-Bernstein expansion to describe the binding energies (ro-vibrational term values) of the ground triplet state a(3)Sigma(+)(u) of alkali metal dimers. The parameters of this description are determined for Rb-2 and Cs-2 molecules. This approach gives a recipe to calculate the whole variety of the binding energies with characteristic accuracies from similar to 1 x 10(-3) to 1 x 10(-2) cm(-1) using a relatively simple algebraic equation. (C) 2014 AIP Publishing LLC.