Charge transfer and association of Na+with87Rb atoms from extremely low to intermediate energies

The nonradiative charge-transfer processes in Na${}^{+}$+${}^{87}$Rb(5$s$) collisions have been investigated by using the quantum-mechanical molecular-orbital close-coupling method and the two-center atomic-orbital close-coupling method for the energy range of 10${}^{\ensuremath{-}4}$--5 and 0.3--100 keV/u, respectively. The radiative charge-transfer, radiative-decay, and radiative-association processes have been investigated by using the fully quantum, optical-potential, and semiclassical methods for the energy range of 10${}^{\ensuremath{-}18}$--0.2 eV/u. The nonradiative charge-transfer processes dominate the collisions for energies above 0.2 eV/u and radiative-decay processes dominate in the lower-energy region. At the very low collision energies of 10${}^{\ensuremath{-}18}$--10${}^{\ensuremath{-}3}$ eV/u, the radiative-association process is more important than the radiative charge-transfer process. Most importantly, it is found that the radiative cross sections exhibit Langevin behavior as ${E}^{\ensuremath{-}1/2}$ for energies less than 10${}^{\ensuremath{-}2}$ eV/u.