  We present a theoretical study of rotationally elastic and inelastic
collisions between molecular nitrogen ions and Rb atoms in the sub-Kelvin
temperature regime prevalent in ion-atom hybrid trapping experiments. The cross
sections for rotational excitation and de-excitation collisions were calculated
using quantum-scattering methods on ab-initio potential energy surfaces for the
energetically lowest singlet electronic channel of the system. We find that the
rotationally inelastic collision rates are at least an order of magnitude
smaller than the charge-exchange rates found in this system, rendering
inelastic processes a minor channel under the conditions of typical hybrid
trapping experiments.
