Collision-induced excitation of ammonia in warm interstellar and circumstellar environments

Abstract Ammonia (NH3) is the first polyatomic molecule detected in interstellar medium. Both its spectroscopic and collisional properties have been extensively studied earlier, NH3 was often used laboratory astrophysics studies to compare high-level scattering calculations with state-of-the-art experiments. Nevertheless, some of important remain unresolved. In this paper we report state-to-state thermally averaged data for rotational excitation by H2 calculated close-coupling quantum theory. nuclear spin symmetries (ortho/para) colliders are studied. Similar research has carried out previously, providing rate coefficients up temperature 200 K states internal energy ∼420 cm−1. Here computed cross sections collision energies 4700 cm−1 500 K. Most rotation-inversion levels ammonia considered below vibrational threshold, leading a total 33 ortho- 62 para-NH3 states. We compared our results most accurate He H atoms available literature. The propensity rules also analysed case high NH3. obtained averaging over thermal relative populations exhibit significantly larger magnitudes than transitions large difference, when transfer between strong.