Electronic structure of eka-thorium (element 122) compared with thorium

The electronic levels of thorium and eka-thorium (element 122) are calculated in the framework of the Dirac-Coulomb-Breit Hamiltonian using a large Gaussian-spinor basis. Correlation is included by the Fock-space or intermediate Hamiltonian coupled-cluster method. The 51 reported levels of thorium and its ions are compared with experiment, giving an average error of 0.062 V for Fock space and 0.051 V for the intermediate Hamiltonian method. Predicted E122 levels are expected to have similar accuracy. The ground state of E122 is 8s 2 7d8p, to be contrasted with 7s 2 6d 2 for Th. Increased relativistic effects in the super-heavy element lead to major differences between the level structure of these two atoms and their ions. The effects of Breit and QED terms are discussed.