Using ab initio methodology, we studied the IO(q+) (q = 2, 3, 4) multi-charged ions. Benchmark computations on the IO(X(2)Π) neutral species allow validate the current procedure. For IO(2+), 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 IO(3+) trication, where a shallow potential well along the IO internuclear distance is computed. This potential well supports more than 10 vibrational levels. The IO(3+) excited states are repulsive in nature, as well as the computed potentials for the IO(4+) 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.
At present, we investigate the structure and the stability of NO(+)Arn (n ≤ 54) ionic clusters using analytical potential functions. The energy of these systems is described using additive potentials with VNO(+)Ar and VAr-Ar representing the pair potential interactions. To find the geometry of the lowest energy isomers of the NO(+)Arn clusters, we use the so-called basin hopping method of Wales et al. which combines a Monte-Carlo exploration and deformation method. The reliability of our model was checked by deriving the structures of the NO(+)Arn systems (n = 1, 2, 3 and 4) using ab initio Moller-Plesset perturbation theory up to second order (MP2) in connection with the aug-cc-pVTZ basis set. Magic numbers for sizes n = 8, 12, 18, 22, and 25 are found and they show a high relative stability. Our results reveal that a transition in the NO(+) ion coordination from 8 (square antiprism) to 12 (icosahedrons) occurs for n = 11. Examination of the stable structures of the ionic clusters demonstrates that the first solvation shell closes at n = 12. Furthermore, we found that the NO(+)Arn (n = 12-54) clusters are structurally very similar to the homogenous rare gas clusters with a polyicosahedral packing pattern. The distribution exhibits an additional magic number at n = 54, consistent with the completion of a second solvation sphere around NO(+). The effects of microsolvation of NO(+) cation in Ar clusters are also discussed. Generally, our results agree with the available experimental and theoretical findings on NO(+)Arn clusters and more generally on diatomics solvated in Ar clusters.
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