Learning from model grids: Tracers of the ionization fraction in the ISM Emeric Bron, Evelyne Roueff, Maryvonne Gerin, Jérôme Pety, Pierre Gratier, Franck Le Petit, Viviana Guzman, Jan Orkisz, Victor de Souza Magalhaes, Mathilde Gaudel et al. (20 more) EPJ Web of Conferences, 265 (2022) 00023 Published online: 07 September 2022 DOI: 10.1051/epjconf/202226500023