Perturbation model for the X1 Σ+ and a3 Σ+ states of NaK at intermediate internuclear distances beyond 6 Å

Abstract

The energy of the X1Σ+ and a3Σ+ states of NaK was estimated from a perturbative model for intermediate- and long-range internuclear distances. Both the charge overlap effects calculated from a model previously published and the exchange contribution estimated from the asymptotic formula were taken into account. Fitted analytical expressions are proposed for electrostatic and induction energy terms as well as for various dispersion damping functions. From comparison with accurate experimental results, the present model is seen to be valid for values of R greater than 6 Å (1 Å = 10−10 m) for the X1Σ+ state and R greater than 8 Å for the a3Z+ state.