SOLIS - XIII. Nitrogen fractionation towards the protocluster OMC-2 FIR4 L. Evans, F. Fontani, C. Vastel, C. Ceccarelli, P. Caselli, A. López-Sepulcre, R. Neri, F. Alves, L. Chahine, C. Favre and V. Lattanzi A&A, 657 (2022) A136 Published online: 21 January 2022 DOI: 10.1051/0004-6361/202142147