Excited states of XH²⁺(X=C, N, O, S) ions: a combined experimental and theoretical study

Excited electronic states of doubly charged molecular ions of the diatomic hydrides CH 2+ , NH 2+ , OH 2+ and SH 2+ are investigated by means of high-resolution translational energy spectrometry. Long-lived states of CH 2+ , NH 2+ and SH 2+ (but not OH 2+ ) are observed. Potential energy functions are calculated using a semi-empirical molecular-orbital technique as well as a high-level ab initio method using large basis sets of at least double zeta plus polarisation quality. Translational energy spectra of singly charged hydride ions are also presented.