Theoretical study of the spectroscopy and the metastability of the NS+cation

The potential energy curves of the NS+ electronic states are computed at the aug-cc-pV5Z/CASSCF/MRCI level of theory. Using these highly correlated wavefunctions, we evaluated their mutual spin–orbit coupling terms and the transition moment evolutions. Then, we deduced an accurate set of spectroscopic constants and investigated the spin–orbit induced predissociation of the lowest electronic excited states of this cation. In particular, we identify a new well-bound quintet state, namely the NS+ (15Π). The NS+(15Π) v'+ ≤ 5 levels decay radiatively to populate the NS+(1 5Σ+) state after emission of visible light, whereas the upper rovibrational levels undergo rapid spin–orbit induced predissociation processes forming S+(4S) and N(4S) fragments via the repulsive 17Σ+ state. The potential energy curve of NS (X2Π) is also computed and used together with those of NS+ electronic states for the prediction of the single ionization spectrum of NS.