Observation of Zr2(2+), Cd2(2+), Hf2(2+), W2(2+), and Pt2(2+) in the gas phase

Five homonuclear diatomic dications Zr(2)(2+), Cd(2)(2+), Hf(2)(2+), W(2)(2+), and Pt(2)(2+) have been observed in the gas phase by mass spectrometry. These exotic doubly positively charged molecules were produced indirectly in the ion extraction region of a secondary ion mass spectrometer during sputtering of zirconium, cadmium, hafnium, tungsten, and platinum metal foils, respectively, by energetic high-current Ar(+) ion surface bombardment. They were detected in positive ion mass spectra at half-integer mz values for ion flight times of the order of approximately 10(-5) s. To our knowledge, these species had not been observed before. This experimental work confirms two theoretical investigations that had predicted that W(2)(2+) and Cd(2)(2+) are long-lived metastable species in the gas phase, but contradicts two theoretical studies that had suggested that Pt(2)(2+) should be unstable with respect to fragmentation. Therefore an advanced theoretical investigation of the ground state of Pt(2)(2+) was also performed. Our calculation shows that the ground state of Pt(2)(2+) is metastable with an internuclear equilibrium distance of 2.36 A, a dissociation energy (with respect to the top of the barrier) of 2.32 eV, and an ionization potential of Pt(2)(+) of about 15.8 eV. The latter theoretical result strongly suggests that Pt(2)(2+) dication formation in our experiment may have taken place via the resonant electron transfer process Pt(2)(+) + Ar(+) --> Pt(2)(2+) + Ar.