A study of long-range covalent--ion-pair coupling in Rb$_2$ and a comparison with Li$_2$

The formation of bound ion-pair states through optical excitation at short-range has been observed in a number of alkali dimers, while the corresponding process due to collisions following excitation at long-range has thus far only been observed between alkali atoms and large molecules of exceptionally high electron affinity [1]. A study of long-range covalent--ion-pair coupling in cold Rb$_2$ and Li$_2$ is presented, including the dependence of this long-range process on parameters such as the initial relative velocity and impact parameter for two different mechanisms [2]. Calculations are based on the well-known Landau--Zener formalism and particular attention has been paid to the regions of parameter space in which the approximations implicit in this approach remain valid. Cross-sections for ion-pair formation are calculated for different channels of the ground- and excited-state atom pair in order to identify possible ``gateway'' states for efficient experimental production of bound ion-pair systems.\\[4pt] [1] M. Cannon and F.B. Dunning, J. Chem. Phys. {\bf 130} 044304 (2009)\\[0pt] [2] M. Cheret and L. Barbier, Phys. Rev. A {\bf 30} 1132 (1984).