We present a theoretical investigation of the electronic structure and properties of radium monochalcogenides, with chalcogens O, S, and Se, as well as the ionic species ${\mathrm{RaO}}^{\pm }$. Our approach combines two different, 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 $[\mathrm{CCSD}\left(\mathrm{T}\right)+\mathrm{X}2\mathrm{C}]$, 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 ($\mathrm{MRCI}+\mathrm{Q}+\mathrm{ECP}+\mathrm{SO}$). The dimers exhibit very large permanent dipole moments and sizable dipolar polarizabilities, while the Franck-Condon factors between the lowest electronic states are highly nondiagonal. These features are discussed in terms of the divalent character of the chemical bonding in the neutral species.

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• Atomic & molecular structure
• Chemical binding
• Electronic transitions
• Long-range interactions
• Potential energy surfaces
• van der Waals interaction