Strong Closed-Shell Interactions: Observed Formation of BaRg(2+) Molecules in the Gas Phase at Room Temperature

Closed shell interactions between the rare gases He Ne; Ar, Kr, and Xe and the Ba2+ dication (isoelectronic with Xe) have been explored both experimentally and computationally. Unprecedented observations are reported for the formation of the diatomic molecules BaHe2+, BaAr2+, BaKr2+, and BaXe2+ in helium bath gas at room temperature in a selected ion flow tube (SIFT) tandem mass spectrometer. The Ba2+ dications were produced by electrospray ionization. Triatomic cations of the type Ba(Rg)(2)(2+) also were recorded with Rg = Ar, Kr, and Xe. Experiment and theory demonstrate that the rate of formation of BaRg(2+) and the strength of the interaction between Rg and Ba2+ increase with increasing polarizability of the rare gas atom.