ION-MOLECULE PROCESSES IN THE INTERSTELLAR-MEDIUM - RATES FOR ROTATIONAL EXCITATIONS IN NH3-H+ COLLISIONS

The collisional excitation of rotational states of NH3 under the inter action with subthermal protons is studied via a sophisticated, fully a nisotropic potential function discussed before and by treating the mul tichannel scattering problem via the coupled-state (CS) approximation. It is found that one rotational level of NH3 exhibits the largest pro bability to get collisionally excited and to be involved in postcollis ional radiative emission at a specific frequency. The limited efficien cy found for the multiple-jump collisional excitation processes also s uggests that, at the temperatures of the interstellar medium, there sh ould be a rather low concentration of rotationally ''hot'' NH3 molecul es.