Analysis of exchange energy at long range for states of alkali diatomic molecules correlating to two ground state atoms

Recently experimentally-based asymptotic exchange energies Delta V-E betwee n ground state atoms in Li-2, Na-2, K-2, and NaK have been determined from spectroscopically-determined potential energy curves. These empirical resul ts are shown to be well fit by the expression -CR(alpha)e(-beta R) of Smirn ov and Chibisov, where C is a positive constant and alpha and beta can be r eadily calculated from the atomic ionization energies. The expression shoul d be useful for estimating the exchange energy in other alkali dimers. (C) 1999 American Institute of Physics. [S0021-9606(99)30335-4].