Excitation of Molecules and Atoms for Astrophysics (EMAA): A spectroscopic and collisional database

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² Univ. Grenoble Alpes, CNRS, OSUG, 38000 Grenoble, France

^★ Corresponding authors: alexandre.faure@univ-grenoblealpes.fr; aurore.bacmann@univ-grenoble-alpes.fr

Received: 6 March 2025
Accepted: 15 July 2025

Abstract

Context. In astrophysical environments, the energy levels of molecules, atoms, and ions are rarely populated at local thermodynamic equilibrium (LTE), that is the level populations reflect the competition between radiative and collisional processes. Interpreting non-LTE spectra therefore requires knowing both the Einstein radiative coefficients and the collisional rate coefficients. For a long time, inelastic collision calculations were limited to the most abundant and simple species, but they have now entered a new era thanks to the increase of computer power and the development of high-accuracy potential energy surfaces.

Aims. With the advent of observatories with powerful spectral capabilities, such as ALMA or the JWST, and the wealth of new species detected, obtaining collisional rate coefficients quickly has become essential. We aim to provide the community with atomic and molecular data available from the literature for an ever-increasing number of systems.

Methods. We have developed a database hosting both the collisional and spectroscopic data necessary to interpret spectra of non-LTE environments such as the (extra)galactic interstellar media, star-forming regions, and cometary atmospheres. We provide data files that can be employed directly in widely used non-LTE radiative transfer codes such as RADEX.

Results. To date, the database contains 106 targets, including nuclear-spin isomers and isotopologues and nine possible projectiles (ortho-H₂, para-H₂, H, H⁺, electrons, He, CO, ortho-H₂ O and para-H₂O, depending on the targets), for a total of 311 target-projectile data files.