An Ab Initio Study Of The Ionization Potentials And F-F Spectroscopy Of Europium Atoms And Ions

The first three ionization potentials of europium and the f-f spectroscopy of the two lowest multiplets of Eu+3 have been calculated using ab initio spin-orbit configuration interaction techniques. To accomplish this, a new averaged relativistic effective core potential has been developed which leaves only the 5s, 5p, and 4f in the valence space. A series of configuration interaction calculations were carried out up through single and partial double excitations with a double-zeta quality basis set. The computed ionization values have an absolute error of about 0.1 eV from the experimental values. The computed f-f spectroscopy for the lowest F-7 multiplet of Eu+3 has a RMS error with experiment of about 100 cm(-1). The computed f-f spectroscopy for the first excited D-5 multiplet has a higher RMS error of about 350 cm(-1). The computed center of gravity separation between the D-5-F-7 multiplet is underestimated by 750 cm(-1). Comparisons between non-spin-orbit and spin-orbit configuration interaction calculations for the separations of the centers of gravity of multiplets are very favorable up through single and double excitations with differences of a tenth of an eV or less. The spin-orbit configuration interaction calculations are among the largest ever performed for lanthanides, with expansion lengths in excess of 1.9 million double-group-adapted functions. The calculations were achieved by application of a new parallel spin-orbit configuration interaction component in the COLUMBUS Program System. (C) 2002 American Institute of Physics.