The role of spin–orbit effects in the mobility of N+ ions moving in a helium gas at low temperature Lamia Aïssaoui, Peter J. Knowles and Moncef Bouledroua Eur. Phys. J. D, 74 7 (2020) 155 Published online: 23 July 2020 DOI: 10.1140/epjd/e2020-10138-0