Theoretical chemistry of superheavy elements E116 and E114

Abstract

RECENT evidence¹ for the presence of primordial superheavy elements 126, 124, 116 and possibly 114 in microscopic crystalline monazite inclusions in biotite micas raises several interesting questions. Earlier work^2,3 suggested reasons why E124 and E126, the homologues of U and Pu, respectively, might occur in such an environment, but gives little information about E116. Better information on both E114 (eka–Pb) and E116 (eka–Po) could enable us to see why they might occur in these minerals and help suggest methods of concentration. At present, ab initio relativistic structure calculations for molecules containing superheavy elements are not feasible. We have developed techniques, however, for studying the structure of heavy atoms and ions using the multi-configuration Dirac–Fock (MCDF) relativistic self-consistent field method⁴; this is a considerable advance on the single configuration Dirac–Fock or Dirac–Slater techniques previously available^2,3. Applications of the MCDF method to atoms and ions of Ba, Hf (Ref. 4), Bi and U, for example, have yielded good ionisation potentials and energy spectra, mainly due to the way in which relativistic effects, which increase dramatically in size with atomic number^2–4, are handled. These effects make it difficult to predict some chemical properties of superheavy elements by extrapolation from the Periodic Table. We use here, therefore, the results of MCDF calculations of some properties to estimate the heat of formation of simple compounds of E114 and E116 with the simple ionic model⁵ and with Pauling's semi-empirical valence-bond resonance model⁶, to acquire insight into the chemistry of these elements.