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 wa s estimated from a perturbative model for intermediate- and long-range internuclear distances. Both the charge overlap effects calculated fr om a model previously published and the exchange contribution estimate d from the asymptotic formula were taken into account. Fitted analytic al expressions are proposed for electrostatic and induction energy ter ms as well as for various dispersion damping functions. From compariso n 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 alph a(3) Sigma(+) state.