Ion-molecule processes in the interstellar medium. Rates for rotational excitations in NH 3-H + collisions

Abstract

The collisional excitation of rotational states of NH 3 under the interaction with subthermal protons is studied via a sophhisticated, fully anisotropic potential function discussed before and by treating the multichannel scattering problem via the coupled-state (CS) approximation, It is found that one rotational level of NH 3 exhibits the largest probability to get collisionally excited and to be involved in postcollisional radiative emission at a specific frequency. The limited efficiency found for the multiple-jump collisional excitation processes also suggests that , at the temperatures of the interstellar medium, there should be a rather low concentration of rotationally “hot” NH 3 molecules.