Electronic properties of the Radium-monochalcogenides RaX (X = O,S,Se) and RaO+/- ions

Abstract

We present a theoretical investigation on the electronic structure and properties of radium monochalcogenides, with chalcogens O, S, and Se, as well as the ionic species RaO +/-. Our approach combines fully relativistic and partially relativistic quantum-chemistry methods. Electronic properties are obtained using the exact two-component Hamiltonian-based coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)+ X2C], while potential energy curves are computed using an internally contracted multireference configuration interaction method, including relativistic effects through small-core pseudopotentials and Pauli-Breit operator diagonalization (MRCI+Q+ECP+SO). The dimers exhibit very large permanent dipole moments and sizable dipolar polarizabilities, while the Franck-Condon factors among the lowest electronic states are highly non-diagonal. These features are discussed in terms of the divalent character of the chemical bonding in the neutral species.

Figures (9)

• Figure 1: The MRCI+Q + ECP potential energy curves of 10 lowest $\Lambda$-S electronic states for the neutral Radium-monochalcogenides: (a) RaO, (b) RaS and (c) RaSe . Solid lines are used for the singlet states, while dashed lines refers to triplet states. The inset zoomed the region in the black box.
• Figure 2: Molecular orbitals for the valence electron in RaO (a,b,c), RaS (d,e,f) and RaSe (g,h,i). The orbitals represents in order the 1$\sigma$,2$\sigma$ and 3$\pi_{1}$ orbitals constituting the X$^{1}\Sigma^{+}$. In all the cases the green atom is Ra, and the divalent stucture of the bond is represented.
• Figure 3: Absolute value of the transition dipole moment for the X$^{1}\Sigma^{+}\longrightarrow$B$^1\Sigma^+$ (blue curves) ,and X$^{1}\Sigma^{+}\longrightarrow$A$^1\Pi$ (blue curves) transitions, in the RaO (Solid lines) and RaS (dahsed lines) molecules.
• Figure 4: Franck-Condon factors of the first five vibrational states for the single-single transitions: (a) X$^{1}\Sigma^{+}\longrightarrow$B$^{1}\Sigma^{+}$ of RaO, (b)X$^{1}\Sigma^{+}\longrightarrow$A$^{1}\Pi$ of RaO, (c) X$^{1}\Sigma^{+}\longrightarrow$B$^{1}\Sigma^{+}$ of RaS and (d)X$^{1}\Sigma^{+}\longrightarrow$A$^{1}\Pi$ of RaO
• Figure 5: Potential energy curves of the lower 6 $\Lambda$-S electronic states for the RaO$^+$ molecular ion. The inset zoomed the black box regions. The axis labels in the inset are omitted because of the space, but they are the same as the big axis