Theoretical study of the electronic structure of the alkaline earth BeLi2+ ion

Abstract

In this work, we present the structural and the spectroscopic properties of the alkaline earth BeLi$^{2+}$ ion for all the electronic states dissociating into Be$^{+}$(2s, 2p, 3s, 3p, 3d, 4s, 4p, and 4d) + Li$^{+}$ and Be$^{2+}$ + Li (2s and 2p). We have used an ab initio approach involving a non-empirical pseudopoential for the Li$^{+}$ and Be$^{2+}$ cores and core-core and core-valence correlation corrections. For our best knoweledge, the adiabatic potential energy curves and the spectroscopic constants for nearly 18 electronic states of $^{2}$Σ $ ^{+}$, $^{2}$Π and $^{2}$ Δ symmetries are determined here for the first time. As neither experimental nor theoretical data are available for BeLi$^{2+}$, our results are discussed and compared with similar systems such as BeH$^{2+}$. Numerous avoided crossings between the electronic states of $^{2}$Σ$ ^{+}$ and $^{2}$Π symmetries have been localised and analysed. Their existences are related to the interaction between the potential energy curves and the charge transfer process between the two ionic systems Be$^{(2+)}$Li and Be$^{+}$Li$^{+}$. Furthermore, we have calculated the adiabatic transition dipole moments from X$^{2}$Σ$ ^{+}$, 2$^{2}$Σ$ ^{+}$ and 3$^{2}$Σ$ ^{+}$ states to the higher electronic states of the same symmetry. This study represents the necessary initial step towards the investigation of the charge transfer processes in collision between Be$^{+}$-Li$^{+}$ and Be$^{2+}$-Li.