Three gas-phase diatomic trications Se-2(3+), Te-2(3+), and LaF3+ have been produced by Ar+ ion beam sputtering of Se, Te, and LaF3 surfaces, respectively. These exotic molecular ions were detected at noninteger m/z values in a magnetic sector mass spectrometer for ion flight times of greater than or equal to13 mus that correspond to lower limits of their respective lifetimes. Se-2(3+) and Te-2(3+) were unambiguously identified by their characteristic isotopic abundances. Ab initio calculations of the electronic structures of Se-2(3+), Te-2(3+), and LaF3+ show that these molecular trications are metastable with respect to dissociation into fragment ions of Se2++Se+, Te2++Te+, and La2++F+, respectively. Their barrier heights are about 0.49, 0.29, and 0.53 eV, and the equilibrium internuclear distances (bond lengths) are about 0.23, 0.27, and 0.26 nm, respectively. The gas-phase diatomic dications Se-2(2+) and Te-2(2+) were also observed and unambiguously identified. They were found to be long-lived metastable molecules as well, whereas LaF2+ is thermochemically stable. (C) 2004 American Institute of Physics.