Small gas-phase dianions of Zn3O42−, Zn4O52−, CuZn2O42−, Si2GeO62−, Ti2O52− and Ti3O72−

Abstract

We have searched for new species of small oxygen-containing gas-phase dianions produced in a secondary ion mass spectrometer by Cs⁺ ion bombardment of solid samples with simultaneous exposure of their surfaces to O₂ gas. The targets were a pure zinc metal foil, a copper-contaminated zinc-based coin, two silicon–germanium samples (Si_1−xGe_x (with x = 6.5% or 27%)) and a piece of titanium metal. The novel dianions Zn₃O₄²⁻, Zn₄O₅²⁻, CuZn₂O₄²⁻, Si₂GeO₆²⁻, Ti₂O₅²⁻ and Ti₃O₇²⁻ have been observed at half-integer m/z values in the negative ion mass spectra. The heptamer dianions Zn₃O₄²⁻ and Ti₂O₅²⁻ have been unambiguously identified by their isotopic abundances. Their flight times through the mass spectrometer are ∼20 μs and ∼17 μs, respectively. The geometrical structures of the two heptamer dianions Ti₂O₅²⁻, and Zn₃O₄²⁻ are investigated using ab initio methods, and the identified isomers are compared to those of the novel Ge₂O₅²⁻ and the known Si₂O₅²⁻ and Be₃O₄²⁻ dianions.