Gas-phase diatomic trications of Se ₂ ³⁺, Te ₂ ³⁺, and LaF ³⁺

Three gas-phase diatomic trications Se ₂ ³⁺, Te ₂ ³⁺, and LaF ³⁺ have been produced by Ar ⁺ ion beam sputtering of Se, Te, and LaF ₃ surfaces, respectively. These exotic molecular ions were detected at noninteger m/z values in a magnetic sector mass spectrometer for ion flight times of ≥13 μs 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 LaF ³⁺ show that these molecular trications are metastable with respect to dissociation into fragment ions of Se ²⁺+Se ⁺, Te ²⁺+Te ⁺, and La ²⁺+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 LaF ²⁺ is thermochemically stable.