  The Rb-NH interaction is investigated as a prototype for interactions between
alkali metal atoms and stable molecules. For spin-aligned Rb and NH that
interact on a quartet surface ($^4A''$), the interaction is relatively weak,
with a well depth of 0.078 eV. However, there are also doublet surfaces of
ion-pair character that are very much deeper (well depth 1.372 eV) and may be
important for atom - molecule collision rates. Similar deeply bound ion-pair
states are likely to exist for other alkali atom -- molecule pairs. It is shown
that a transition to a dipolar superfluid phase will be easier to achieve for
low-mass than for high-mass species.
