Neptunium ionization potentials

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. 

Figure 4. Neptunium photoionization threshold spectrum. The excitation scheme is shown at the left. The threshold at 4593 A is marked by the onset of very strong autoionization peaks. It yields an ionization potential of 50 518 cm 1...

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case of neptunium, the presence of two series converging to limits 24 cm - - apart (see Fig. 6) helps to confirm the unpublished value.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. 

Rauh, E. G. and Ackermann, R. J., "The first ionization potentials of neptunium and neptunium monoxide,"... 

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