  Rate constants for the charge transfer reaction between N${}_{2}$H${}^{+}$
and Rb in the mK regime are measured in an ion-atom hybrid trap and are found
to be lower than the Langevin capture limit. Multireference ab initio
computation of the potential energy surfaces involved in the reaction reveals
that the low-temperature charge transfer is hindered by short-range features
highly dependent on the collision angle and is promoted by a deformation of the
molecular frame. The present study highlights the importance of polyatomic
effects and of stereodynamics in cold molecular ion-neutral collisions.
