Theoretical investigations of the IO,^q+ (q = 2, 3, 4) multi-charged ions: Metastability, characterization and spectroscopy

Using ab initio methodology, we studied the IO^q+ (q = 2, 3, 4) multi-charged ions. Benchmark computations on the IO(X²Π) neutral species allow validate the current procedure. For IO²⁺, several potential wells were found on the ground and the electronic excited states potentials with potential barriers with respect to dissociation, where this dication can exist in the gas phase as long-lived metastable molecules. We confirm hence the recent observation of the dication by mass spectrometry. Moreover, we predict the existence of the metastable IO³⁺ trication, where a shallow potential well along the IO internuclear distance is computed. This potential well supports more than 10 vibrational levels. The IO³⁺ excited states are repulsive in nature, as well as the computed potentials for the IO⁴⁺ tetracation. For the bound states, we give a set of spectroscopic parameters including excitation transition energies, equilibrium distances, harmonic and anharmonic vibrational terms, and rotational constants. At the MRCI + Q/aug-cc-pV5Z(-PP) level, the adiabatic double and triple ionization energies of IO are computed to be ∼28.1 eV and ∼55.0 eV, respectively.