Context: .Observations of deuterated molecules are useful probes of the physical and chemical conditions in star-forming regions. However their detailed interpretation is hampered by the lack of knowledge of the corresponding collisional rate coefficients.
Aims: .We extend our previous study of ammonia collisional excitation by helium to monodeuterated ammonia NH2D, which has been found to be abundant in a variety of environments.
Methods: .We introduce the principal isotopic effects in the collisional equations by calculating the relevant angular dependence of the intermolecular potential energy surface.
Results: . Cross sections are calculated in the coupled states approximation, and collisional rate coefficients are given from 5 to 100 K, a range of temperatures that is relevant in the interstellar medium.
Conclusions: .These results allow to include justifiable collisional excitation rate coefficients of NH2D by He in the analysis of the emitted radiation for the first time