An accurate set of H3O+ ? H2 collisional rate coefficients for non-LTE modelling of warm interstellar clouds

ABSTRACT Hydronium (H3O+) was first detected in 1986 interstellar molecular clouds. It reported many Galactic diffuse and dense regions, as well extragalactic sources. H3O+ plays a major role both oxygen water chemistry. However, despite the large number of observations, its collisional excitation investigated only partially. In this work, we study state-to-state rotational (de-)excitation ortho- para-H3O+ collisions with para-H2. The cross sections are calculated within close-coupling formalism using highly accurate potential energy surface developed for system. rate coefficients computed up to kinetic temperature 300 K. Transitions between lowest 21 rotation-inversion states were studied para-H3O+, 11 ortho-H3O+, i.e. all levels energies below 430 K (?300 cm?1) considered. order estimate impact new on astrophysical models H3O+, radiative transfer calculations also carried out. We have examined how data affect line intensities respect older previously used interpretation observations. By analysing transitions find that our new, significant (typically factor 2) radiation temperatures, allowing more estimation column densities relative abundances hydronium, especially warm clouds, paving path towards better