Theoretical investigation of the alkali-dimer cation K 2 + : Potential energy, dipole moment and atomic polarizabilities

Abstract

The potential energy curves of the electronic states of $^{2}$Σ$^{+}_{g, u}$, $^{2}$Π$ _{g, u}$ and $^{2}$Δ$_{g, u}$ symmetries of the K$_{2}^{+}$ molecular ionic system dissociating into K (4s, 4p, 5s, 3d, 5p, 4d and 6s) + K$^{+}$, have been calculated. The computation was performed using an ab initio approach, where a non-empirical pseudopotential for the K$^{+}$ core has been involved and a core-core and core valence correlation corrections have been added. The spectroscopic constants have been derived and compared with the available theoretical and experimental works. A good agreement has been obtained for the ground and the first excited states. However, a clear disagreement between this study and the model potential work of Magnier and Aubert-Frecon [J. Quant. Spect. Rad. Trans. 78, 2003] has been observed for several excited states. They found that the 5$^{2}$Σ$^{+}_{u}$, 6$^{2}$Σ$^{+}_{g}$, 6$^{2}$Σ$^{+}_{u}$, 7$^{2}$Σ$^{+}_{g}$, 7$^{2}$Σ$^{+}_{u}$, 4$^{2}$Π$_{g}$ and 2$^{2}$Δ$_{u}$ states are repulsive, although they are attractive with potential well depths of 10, 100 and 1000 cm$^{-1}$ in our study. Furthermore, the atomic polarizabilities have been predicted from a vibrational spacing analysis based on the WKB approximation applied on the potential energy at long-range distances. These polarizabilities have been used to reproduce the long range potential interaction for some electronic states.