Ultra low-energy behavior of an ionic replacement reaction (HeHe+)-He-3-He-4+He-4 -> He-4(2)++He-3

An accurate ab initio potential energy surface has been employed for the treatment of the full quantum dynamics for isotopic exchange reaction (HeHe2+)-He-4-He-3+He-4. State-to-state reactive probabilities have been obtained using a time-independent approach at ultralow collision energies. More than one total angular momentum has been calculated in order to provide a converged rate constant for the title reaction within the ultralow temperature regime. The reaction is found to become faster than the Langevin value when T -> 0, thus providing connection with experiments with sympathetically cooled molecular ions or superfluid helium nanodroplets