Superheavy Elements – Chemistry and Spectroscopy

Abstract

Superheavy elements, a somewhat loose term usually applied to elements with atomic number above 100, exhibit chemical and spectroscopic properties that are not necessarily extrapolations of lighter elements in the same group of the periodic table. This behavior is caused by relativity, which already affects heavy elements (e.g., changing transition energies in gold by as much as 4 eV), and is more important for the superheavy atoms. These elements are produced in accelerators in minute quantities and have short lifetimes, making experimental studies very difficult and costly. Chemical experiments involving the heavier elements are of the ‘one‐atom‐at‐a‐time’ type. Input from theory is crucial in guiding the experimentalist in the search for data. The various theoretical and computational methods used to study these elements are described, and representative results given. For atoms, one can use highly accurate methods: starting from the four‐component Dirac–Coulomb–Breit Hamiltonian, correlation may be included by the most powerful tools of quantum chemistry. In particular, the relativistic Fock‐space coupled cluster (CC) approach reproduced numerous energy levels of heavy elements with an accuracy of a few hundredths of an eV, and provides therefore a reliable tool for predicting yet unknown levels of superheavy elements, as well as their ground state electron configurations. Molecules present a more difficult computational challenge, and more approximate methods, relying on effective core potentials or density functionals, are often used. Molecular properties such as volatility or adsorption energies, which are needed to guide experimentalists in tracing the compounds produced when atoms synthesized in the accelerator are reacted with various chemicals, are calculated, providing invaluable help in determining the existence and properties of the superheavy elements.