Excited State Atom-Ion Charge-Exchange

We theoretically investigate the exothermic charge-exchange reaction between an excited atom and a ground-state positive ion. In particular, we focus on MOT-excited Ca*(4s4p $^1$P) atoms colliding with ground-state Yb$^+$ ions, which are under active study by the experimental group of E. Hudson at UCLA [1]. Collisions between an excited atom and an ion are guided by two major contributions to the long-range interaction potentials, the induction $C_4/R^4$ and charge-quadrupole $C_3/R^3$ potentials, and their coupling by the electron-exchange interaction. Our model of these forces leads to close-coupling equations for multiple reaction channels. We find several avoided crossings between the potentials that couple to the nearby asymptotic limits of Yb*+Ca$^+$, some of which can possibly provide large charge exchange rate coefficients above 10$^{-10}$ cm$^3/$s. [1] W. G. Rellergert, S. T. Sullivan, S. Kotochigova, A. Petrov, K. Chen, S. J. Schowalter, and E. R. Hudson, Phys. Rev. Lett. 107, 243201 (Dec 2011).