On the stability and lifetime of GaO2+ in the gas phase
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The electronic structure, stability, and lifetime of GaO2+ have been investigated using high-level ab initio calculations. The potential energy curves have been calculated at the CCSD(T)/aug-cc-pV5Z and at the MS-CASPT2/ANO-RCC levels of theory. Lifetimes were evaluated using the Exterior Complex Scaling (ECS) method and B-spline basis functions. Our calculations show that GaO2+ is a metastable species in the gas phase, since the diatomic dication, in its ground state, lies 97.1 kcal/mol above the Ga+ (1S) + O+ (4S) dissociation limit. However, the energy barrier that has to be overcome to reach this limit is 3 kcal/mol high so that five vibrational resonances can be accommodated between the bottom of the well and the top of the barrier. The evaluated lifetimes vary from hundreds of femtoseconds to approximately 1 s, so at least two of them have long enough lifetimes (1 s and 91 μs) to be detected using mass spectrometry techniques, in agreement with the experimental evidence. In the experiment (Fiser et al. in Eur J Mass Spectrom 15:315–324, 2009), GaO2+ was observed for an ion flight time of about ~12 μs through a magnetic-sector mass spectrometer and unambiguously identified by its isotopic abundance. Our results also show that isotopic effects on the resonances’ energies and on their lifetimes, when 70Ga is replaced by 69Ga or 71Ga, are very small (~0.1 and ~1%, respectively), reflecting the large mass of the system.
KeywordsDoubly charged species Lifetimes Ab initio calculations Coulomb explosion GaO Gas phase
We thank Klaus Franzreb for sending us his experimental results (ref.16) and his suggestion to calculate GaO2+. This work has been partially supported by the DGI Project No. CTQ2009-13129-C01, by the Project MADRISOLAR2, Ref.: S2009PPQ/1533 of the Comunidad Autónoma de Madrid, by Consolider on Molecular Nanoscience CSC2007-00010, and by the COST Action CM0702. IC and AP gratefully acknowledge a Juan de la Cierva post-doctoral contract from the Ministerio de Ciencia e Innovación of Spain. A generous allocation of computing time at the CCC of the UAM is also acknowledged.
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