INTERATOMIC POTENTIAL MODEL FOR ION-ATOM SYSTEMS INCLUDING A CHARGE-EXCHANGE CONTRIBUTION

A model for the interatomic potential between alkali ions and rare-gas atoms accounting for repulsive and attractive exchange forces has been calculated. The attractive exchange contribution is estimated using Mulliken's charge-transfer theory. The repulsive potential is calculated using Firsov's theory of interacting Thomas-Fermi-Dirac atoms. Two models, φ(R)=ARn-BR4-CR6 (12-4-6 model), and φ(R)=ARn-BR4-CR6+ΔECT (exchange model), were used to calculate the interatomic potential for all the alkali-ion-rare-gasatom combinations. A comparison shows that the charge-exchange contribution ΔECT-[2S2(1+S2)](EA+)2(IB+BR4+CR6-EA+), where EA+ is the electron affinity of the ion, IB is the ionization potential of the atom, B and C are the coefficients of the polarization interaction terms, and S is the two-center overlap integral between the outer orbitals, enhances the long-range attraction and increases the well depth by about a factor of 5 over the 12-4-6 model. The predictions of the classical rainbow scattering angle for the Cs+/Ar case are compared for the two models. The difference in the two calculated rainbow angles strongly suggests that low-energy elastic-scattering angular distributions would be a valid test of the assumptions used in the charge-exchange model. © 1969 The American Physical Society.