The gas-phase diatomic dication SiO2+ has been observed by mass spectrometry and identified by its isotopic abundance. It was produced by energetic, high-current oxygen (O-16 ) ion beam sputtering of a silicon surface and survived a flight time of similar to 10 (5) s. In addition, a detailed theoretical study of SiO2+ has been performed. Our calculations show that SiO2+ is a metastable species with a large potential barrier towards dissociation (similar to 1.55 eV for the SiO2+ X ground state). We have derived a set of accurate spectroscopic constants and transition energies for SiO2+. The adiabatic double ionization energy of SiO is similar to 31 eV. (C) 2009 Elsevier B. V. All rights reserved.