  We carry out quantum inelastic scattering calculations of collisions of Rb
atoms with inverting NH3 and ND3 molecules in the energy range between 0 and
100 cm-1, which are important for experiments using velocity-controlled
molecular beams to probe scattering resonances. We focus on molecules initially
in the upper level of the ammonia inversion doublet, which are
low-field-seeking and can be controlled in a Stark decelerator. We calculate
the integral elastic and state-to-state inelastic cross sections in the coupled
states approximation. We demonstrate the presence of both shape and Feshbach
resonances in the elastic and inelastic cross sections at low collision
energies and discuss their origin in terms of the bound states of Rb--ND3
complex. We also consider elastic and inelastic cross sections in the ultracold
regime, using close-coupling calculations, in order to assess the viability of
sympathetic cooling of ND3 by Rb. The inelastic cross section for relaxation to
the lower level of the inversion doublet is smaller than expected for such a
strongly coupled system, but is still likely to be too large to allow
sympathetic cooling for ND3 in low-field-seeking states. However, there is a
good prospect that sympathetic cooling will be possible for molecules in
high-field-seeking states, even when the collision partner is a magnetically
trapped atom in a low-field-seeking state.
