Collisional excitation of doubly deuterated ammonia NHD2 by para-H2
  Collisional de-excitation rates of partially deuterated molecules are
different from the fully hydrogenated species because of lowering of symmetry.
We compute the collisional (de)excitation rates of ND2H by ground state
para-H2, extending the previous results for He- lium. We describe the changes
in the potential energy surface of NH3- H2 involved by the pres- ence of two
deuterium nuclei. Cross sections are calculated within the full close-coupling
ap- proach and augmented with coupled-state calculations. Collisional rate
coefficients are given between 5 and 35 K, a range of temperatures which is
relevant to cold interstellar conditions. We find that the collisional rates of
ND2H by H2 are about one order of magnitude higher than those obtained with
Helium as perturber. These results are essential to radiative transfer
modelling and will allow to interpret the millimeter and submillimeter
detections of ND2H with better constraints than previously.
