Rotational equilibrium of C2 in diffuse interstellar clouds - II. Formation-excitation at work? J. Le Bourlot, E. Roueff, S. R. Federman, A. M. Ritchey and D. L. Lambert A&A, 699 (2025) A217 Published online: 14 July 2025 DOI: 10.1051/0004-6361/202554760