Are helionitronium trications stable?

In a recent article [Olah, G. A., Prakash, G. K. S. & Rasul, G. (1999) Proc. Natl. Acad. Sci. USA 96, 3494–3495] the authors found that the helionitronium trication, HeNO [Formula: see text] , is an unusually stable helium-containing polyatomic ion. This result was based on second-order many-body perturbation (MP2) calculations that showed that strong binding should occur between the oxygen and helium atoms in the assumed singlet ground state. The dissociation energy with respect to NO(+) and HeO(2+) was predicted to be 7.95 eV. We show here by thorough multireference configuration interaction (MRCI) studies that the ground state for the helionitronium trication is a triplet (3)B(1) state with He binding to the N atom (C(2v)). The He—O bound structure of C(s) symmetry is not stable. Dissociation of the helionitronium trication occurs toward NO [Formula: see text] and He(+), and the trication is bound by at most 0.25 eV. These results indicate that the helionitronium trication is unstable under ambient conditions. The discrepancies between our results and the previous study are explained by the strong multireference character of the wave function of the trication.