Rn-like actinide ions

An interesting case for study involves the Rn- or Fr-like actinide ions. The importance of the spectra for at least two systems, U + and Th +, was discussed recently [67]. Among other properties, Hanni et al. [67] analyzed the difference between U + and Th + polarizabilities, ascribing it to differences in electronic spectra, particularly of highly excited metastable states. To check this assumption, precise measurements or calculations of excited states of the Rn- and Fr-like ions energy levels are necessary. Knowing the electronic spectta 

The relativistic IHFSCC approach was used in 2001 to calculate the spectra of neutral Xe and Rn atoms, obtaining unprecedented and still unsurpassed accuracy, with an average error of 0.6% for the lowest excitation energies (about 20 per atom) [74]. This accuracy allowed predictions, e.g., for the unobserved states of Rn. It was demonstrated that only the combination of using large active spaces with all-order treatment of dynamic correlation in the framework of a high-quality relativistic Hamiltonian can yield such high level of accuracy. 

Our preliminary second order (PT2) calculations, as well as results of Safronova and Safronova [76], show that at least the first 52 excited states in Rn-like Ac, Th, Pa, and U ions are predominantly mixtures of the Xe Af 5d ( ()p nl and Xs Af 5d )S()p nl states. The model spaces were constructed with this in mind. The spaces for both basis sets included 6s and 6p as valence holes, from which electrons are excited. The valence particles, to which electrons are transferred, were in basis A 5/, 6d, Is and Ip, with the main Pm space including excitations from 6p to 5/ and 6d other excitations are in the intermediate space Pi. This gives a total of 55 states. The n values are lower by one in the La ion calculations. In the larger basis B, used here for La only, the valence particles were 6-85, 6-8p, A-6d, 4-6/, and 5g, yielding 912 determinants in P, which give rise to 172 J levels. Obviously, 

4 Electronic Spectrum of Superheavy Elements Nobelium (Z=102) and Lawrencium (Z=103) 

As is well known, the effect of relativity increases when we go to superheavy elements. This term is usually applied to elements with atomic numbers above 100 (trans-fermium elements). The spectroscopic study of superheavy atoms presents a severe challenge to the experimentalist. An important relativistic effect involves changes in the level ordering. 

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