Neptunium Rydberg series

The Rydberg series and photoionization thresholds obtained have permitted the accurate determination of ionization limits for uranium, (1) neptunium, and ten lanthanides. Q)... 

Figure 6. Rydberg series in neptunium obtained by field ionization (double arrow) of laser-excited levels. The excitation scheme is shown on the figure. The spectrum contains two series, one converging to the 5f+6d7s7L5 ground state and the other convering to the % level at 24.27 cm 1 in the ion. For the series converging to the 5li level, the Rydberg level positions with n less than 40.7 (short markers) are calculated using a constant fractional defect of 0.3 (4).

Ionization potentials of 6.1941(5) eV for uranium i and 6.2657(6) eV for neptunium ) have been derived from observed Rydberg series using laser techniques and the method described above. These are the most accurate ionization potentials available for actinide elements. Series converging to the first excited state and to the ground state of the ion were observed for both elements. In the case of neptunium, the presence of two series converging to limits 24 cm - - apart (see Fig. 6) helps to confirm the unpublished value. ) for the interval between the two lowest levels of neptunium. 

Discussion of Actinide Ionization Potentials. The ionization potentials of actinides determined by laser techniques are given in Table IV together with values determined by surface ionization, appearance potential and semi-emperical methods. For uranium, all values are low compared with the values determined by laser techniques with the exception of the surface ionization value by Smith and Hertel.(z ) The spectroscopic values by Sugar jL were obtained from the 5f 7s - 5f 7s8s intervals interpolated from intervals known for the higher actinides. Except for Sugar s value, all the neptunium ionization potential values are low relative to the more accurate values determined by laser methods. The Rydberg series values are the preferred ionization potentials. 

Lemire, R.J., J.Fuger, H. Nitsche, P. Potter, M.H. Rand, J. Rydberg, K. Spahiu, J.C. Sullivan, W.J. Ull-man, P. Vitorge, and H. Wanner. 2001. Chemical thermodynamics series. Vol. 4. Chemical thermodynamics of neptunium and plutonium. Nuclear Energy Agency, Oig. Econom. Coop. Develop. Elsevier, New York. 

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