Electronic spectroscopy of heptacene ions in the search for carriers of diffuse interstellar bands Miriam Kappe, Arne Schiller, Fabio Zappa, Serge A. Krasnokutski, Marie S. Wagner, Holger F. Bettinger and Paul Scheier A&A, 672 (2023) A4 Published online: 23 March 2023 DOI: 10.1051/0004-6361/202244310