PERTURBATION MODEL FOR THE X(1)SIGMA(+) AND ALPHA(3)SIGMA(+) STATES OF NAK AT INTERMEDIATE INTERNUCLEAR DISTANCES BEYOND 6 ANGSTROM

The energy of the X(1) Sigma(+) and alpha(3) Sigma(+) 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 Angstrom (1 Angstrom = 10(10) m) for the X(1) Sigma(+) state and R greater than 8 Angstrom for the alpha(3) Sigma(+) state.