Transition energies of mercury and ekamercury (element 112) by the relativistic coupled-cluster method

The relativistic coupled-cluster method is used to calculate ionization potentials and excitation energies of Hg and element 112, as well as their mono- and dications. Large basis sets are used, with l up to 5, the Dirac-Fock or Dirac-Fock-Breit orbitals found, and the external 34 electrons of each atom are correlated by the coupled-cluster method with single and double excitations. Very good agreement with experiment is obtained for the Hg transition energies, with the exception of the high ({}12 eV) excitation energies of the dication. As in the case of element 111 [Eliav et al., Phys. Rev. Lett. 73, 3203 (1994)], relativistic stabilization of the 7s orbital leads to the ground state of 112⁺ being 6d⁹7s², rather than the d¹⁰s ground states of the lighter group 12 elements. The 112²⁺ ion shows very strong mixing of the d⁸{s}²$, ${d}⁹$s, and ${d}¹⁰$ configurations. The lowest state of the dication is 6${d}⁸$7${s}²$ J=4, with a very close (0.05 eV) J=2 state with strong ${d}⁸s² and d⁹s mixing. No bound states were found for the anions of the two atoms.