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Many-electron effects in the X-ray photoemission spectra of the actinides : a comparison with the rare
earths
S. Kowalczyk
To cite this version:
S. Kowalczyk. Many-electron effects in the X-ray photoemission spectra of the actinides : a com- parison with the rare earths. Journal de Physique Colloques, 1979, 40 (C4), pp.C4-224-C4-225.
�10.1051/jphyscol:1979470�. �jpa-00218866�
JOURNAL DE PHYSIQUE Colloque C4, supplément au n° 4, Tome 40, avril 1979, page C4-224
Many-electron effects in the X-ray photoemission spectra of the actinides : a comparison with the rare earths
S. P. Kowalczyk
Max-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, D-7000 Stuttgart 80, F.R.G.
Résumé. — A partir d'une tendance systématique dans les spectres de photoémission X des terres rares et des éléments voisins, nous suggérons que les niveaux 5s, 5p3/2 et 4d dans les actinides peuvent présenter de forts effets à plusieurs électrons ; des données disponibles sur les actinides permettent de confirmer les prédictions précédentes.
Abstract. — On the basis of systematic trends in X-ray photoemission core-level spectra of the rare earth elements and the adjacent elements, it is suggested that the 5s, 5p3/2 and 4d levels of the actinides should exhibit strong many-electron effects. The available actinide data appears to support the above predictions.
1. Introduction. — A X-ray photoemission (XPS)
spectrum can be considered for many purposes as being representative of a one-electron eigenvalue spectrum. However, it is well known that many- electron (ME) effects are present in XPS [1]. Often these effects are treated in an ad hoc manner or looked on as being a minor perturbation — i.e.
relaxation shift [1], core-level asymmetry [2], appearance of correlation satellites [3], etc. there are also more drastic cases, where ME effects may obliterate the one-electron picture to the extent that it becomes meaningless (and misleading) to speak of a core level in terms of its one-electron quantum numbers [3-5]. It is of interest to study the evolution
of ME effects by observing these effects in a series of elements with similar and systematically varying electronic structure. The rare earth elements form one such series. The systematics of the rare earths illuminate many aspects of ME effects and suggest that other areas of the periodic table may be particularly fertile in ME effects. In this paper, we shall examine recent actinide data [6, 7] in the light of rare earth systematics.
2. Discussion. — We shall limit our discussion to two cases, which the rare earth work suggest as being particularly susceptible to ME effects : a) the relative role of ME effects in the actinide n s level (n = 4, 5, 6) multiplet splittings and correlation satellites and b) the possibility of similar strong dynamical collective effects as observed in the 4p levels in the rare earth elements and the preceding elements [5].
Multiplet splitting is now a well established and highly useful phenomenon in XPS core levels from systems which possess unpaired outer electrons [8].
From work on n s (n = 2 , 3) levels in 3d transition metal compounds and n s (n = 4 , 5) levels in rare
earth systems, it is clear that ME effects are impor- tant and lead to reduced splittings with respect to one-electron predictions in the case where n is the same for the s core level and the outer level with the unpaired spin. For s-levels with principal quantum number different than that of the outermost un- paired level, one electron theory predicts quite well the multiplet splitting. In the cases of reduced split- tings, as expected by sum rule consideration, corre- lation satellites appear. It is noteworthy that such correlation satellites seem in general to occur for outermost s-core levels even in systems which do not exhibit multiplet splitting [9]. Thus we would expect in the case of actinides that a) the 5s levels, which would have multiplet splitting due to interac- tion with unpaired 5f electrons, would have split- tings considerably smaller than expected on the basis of one electron theory, while 4s and 6s levels would exhibit the expected splitting and b) the 5s level should also possess a correlation satellite, even in cases with completely empty 5f levels. Presently there is no data with respect to point a ) . However, with respect to point b), the Th data of Bancroft et
al. [6] does exhibit correlation satellites. Since multi-plet splitting for s-levels in the actinides is dependent on the exchange integral G
3( n s , 5f), the observed splittings should be sensitive to the derealization of the 5f levels.
The second case we wish to pursue is the evolu- tion of the collective effects observed in the 4p spectra of the elements 45 =s z =s 72 [3-5] and the possibility of the existence of similar effects in actinide core levels. For reference, we note that Wendin and colleagues have discussed the mecha- nism of these effects in detail within the framework of diagrammatic many-body perturbation theory [10]. For our purposes the phenomenological ap- proach of figure 7 [5] is suitable. The work of [5]
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979470
MANY-ELECTRON EFFECTS I N THE X-RAY PHOTOEMISSION SPECTRA C4-225
3. Conclusions.
-
Many-electron effects are im- portant in actinide spectra and must be considered when interpreting core-level binding energies, split- tings and shapes. Using knowledge obtained from investigations of other systems, it is predicted that the 5s, 5p,,, and the 4d levels of the actinides should be strongly affected byME
effects. Examination of the available actinide data seems to be in accordance with the above prediction.showed that the development and evolution of the - effect in the 4p levels resulted from the variation and
juxtaposition in energy of several levels. Figures 1
600 -
and
2
indicate that in fact such effects should occur in the Sp,,, level (throughout the series) and 4d (inpossibly a small portion of the series) levels in the
-
actinides. The T h data [6] agrees quite well with the 2
-
above predictions and the Sp,,, data for U and
Pu
[7] 2. p 400 -again support the above prediction. Further data of w a3
high quality of these and other core levels for the -
.-
oactinide series are necessary t o fully appreciate the e
0
development of ME effects in this series. One final 200 - -
Acknowledgments.
-
Beneficial discussions withAlorn~c number Goran Wendin are gratefully acknowledged, a s well
as the support of the Alexander von Humboldt Fig. 1. -Orbital energies from [12] as a function of z. Stiftung.
point worth mentioning is that the binding energies of levels which are effected by ME effects are greatly stabilized. Thus levels, which are perturbed by ME effects, exhibit anomalous discrepancies,
References
- -
[I] SHIRLEY, D. A . , in Photoelectron Spectroscopy o f Solids, ed.
M . Cardona and L. Ley, Springer Tracts Appl. Phys. 26 (1978) Ch. 4.
123 WERTHEIM, G. K., CITRIN, P. H., in reference [I], Ch. 5.
[3] KOWALCZYK, S. P., Ph. D. Thesis, University of California, Berkeley, Lawrence Berkeley Laboratory Report LBL- 4319 (January 1976) unpubl.
[4] GELLIUS, U., J. Electron. Spectrosc. 5 (1974) 985.
[ 5 ] KOWALCZYK, S. P., LEY, L., MARTIN, R. L., MCFEELY,
F. R . , SHIRLEY, D. A., Faraday Discuss. 60 (1975) 7.
[6] BANCROFT, G. M., SHAM, T. K., LARSSON, S., Chem. Phys.
Lett. 46 (1977) 551.
[7] VEAL, B. W., LAMM, D. J., DIAMOND, H., HOEKSTRA, H. R . , Phys. Rev. B 15 (1977) 2929 ;
when compared with theory. This has been shown 9: 811
'
813 ' 815 ' 817 ' 819 ' 91
for the case of the 4s and 4p levels in Xe [4] and for Alom~c number
several of the elements in the series 48 6 z 59 Fig. 2. Orbital energies from [12] as a function of 2.
[ I l l . This serves as a good indicator of ME effects.
VEAL, B. W., LAMM, D. J., CARNAI.L, W. T., HOEKSTRA, H. R., Phys. Rev. B 12 (1975) 5651.
183 KOWALCZYK, S. P., LEY, L., POLLAK, R. A., MCFEELY, F. R., SHIRLEY, D. A., Phys Rev. B 7 (1973) 4009.
[9] MARTIN, R. L., KOWALCZYK, S. P., SHIRLEY, D. A., J.
Chem. Phys. 68 (1978) 3829.
[lo] WENDIN, G., OHNO, M., LUNDQUIST, S., Solid State Commun. 19 (1976) 165 ;
WENDIN, G., OHNO, M., Phys Scr. 14 (1976) 148.
[ l l ] KOWALCZYK, S. P., unpublished results.
[12] Lu, C. C., CARLSON, T. A., MALIK, F. B., TUCKER, T. C., NESTOR, C. W., Atomic data 3 (1971) 1 .
