Thermodynamically stable diatomic dications: The cases of SrO2+ and SrH2+

Abstract

A high level theoretical investigation of the low-lying electronic states of the diatomic dications SrO and SrH is presented for the first time along with experimental results of their mass spectra where they were detected. A global and reliable picture of the potential energy curves of the electronic states and the associated spectroscopic parameters provide quantitative results attesting to the thermodynamic stability of both species. Inclusion of spin-orbit interactions does not significantly change the energetic characterization. For SrO, the ground (X Σ) and first excited (A Π, T = 3971 cm) states are bound (D) by 15.94 kcal mol and 4.71 kcal mol, respectively. Transition probabilities (A) have been evaluated and radiative lifetimes estimated for the vibrational states of A Π (v'), and transition probabilities are expected to be diagonally dominant and fall in the far-IR region of the spectrum. For the singlet states aΔ, b Π, cΣ, and d Σ, transition probabilities have also been calculated for all symmetry allowed transitions and the radiative lifetimes evaluated for selected vibrational states of the upper levels. The transitions associated with the band systems d Σ-b Π and dΣ-c Σ, although falling in the yellow region of the spectrum, with overlapping bands, are expected to show quite distinct intensities since the transition moment associated with d Σ-c Σ is much larger. For singlet transitions, the prediction of relative intensities using the Franck-Condon approximation fails in most of the cases. For SrH, only the ground state is bound (D = 6.54 kcal mol); with an equilibrium distance of 5.117 a, the associated spectroscopic parameters (ω, ωx, B) turned out to be (518.9, 32.77, 2.3227) in cm. For both species, dipole moment functions illustrate the variation of the molecular polarity with the internuclear distance.

Production and Characterization of Molecular Dications: Experimental and Theoretical Efforts

“…More recently, it deserves mention the interesting work by Franzreb et al who were able to produce a variety of oxygen-containing diatomic dications XO 2+ (X = As, Ga, Sb, Ag, Cr, Be) in the gas phase [ 52 ], the metastable ClO 2+ and ClO 3+ ions [ 53 ], and the thermodynamically stable SrO 2+ and SrH 2+ [ 54 ]…”

“…Later, in 1995, van der Kamp et al [51] were able to perform the first charge-transfer reaction between alkali atoms and both CO 2+ and NO 2+ dications. More recently, it deserves mention the interesting work by Franzreb et al who were able to produce a variety of oxygen-containing diatomic dications XO 2+ (X = As, Ga, Sb, Ag, Cr, Be) in the gas phase [52], the metastable ClO 2+ and ClO 3+ ions [53], and the thermodynamically stable SrO 2+ and SrH 2+ [54] Finally, it has to be pointed out the important contribution provided by J.H.D. Eland's research group in the last decades, which has studied and characterized a large number of molecular dications of increasing complexity through the use of the double photoionization combined with electron-ion-ion coincidence techniques [55][56][57][58].…”