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PARTIAL AND TOTAL PHOTOIONIZATION CROSS SECTIONS OF ATOMIC Ba, La AND Ce IN THE
RANGE OF THE GIANT 4d RESONANCES
D. Handschuh, M. Meyer, M. Pahler, T. Prescher, M. Richter, B. Sonntag, H.
Wetzel
To cite this version:
D. Handschuh, M. Meyer, M. Pahler, T. Prescher, M. Richter, et al.. PARTIAL AND TOTAL PHOTOIONIZATION CROSS SECTIONS OF ATOMIC Ba, La AND Ce IN THE RANGE OF THE GIANT 4d RESONANCES. Journal de Physique Colloques, 1987, 48 (C9), pp.C9-539-C9-542.
�10.1051/jphyscol:1987989�. �jpa-00227410�
Colloque C9, supplbment n012, Tome dbcembre
PARTIAL AND TOTAt PHOTOIONIZATION CROSS SECTIONS OF ATOMIC Ba, La AND Ce I N THE RANGE OF THE GIANT 4d RESONANCES
D. HANDSCHUH, M. MEYER,, M. PAHLER, T. PRESCHER, M. RICHTER, B. SONNTAG and H.E. WETZEL
XI. Institut fifr Experimentalphysik, Universit&t Hamburg, Luruper Chaussee 149, 0-2000 Hamburg 50, F.R.G.
Abstract
Total and partial (4d-l, 4f-l, 5s-', 5p-l, 5d-', 6s-l) cross sections of atomic Ba, La and Ce have been determined by absorption and photoelectron spectroscopy in the range of the giant 4d + (4f, ~ f ) resonances. Many electron theories, which take polarization and relaxation effects into account, succeed to describe the gross fea- tures of the spectra, but in many cases fail to reproduce the exact energy posi- tions, line shapes and amplitudes of the resonances in the cross sections of the main and satellite lines.
Introduction
Since their discovery the 4d + (4f, ~ f ) giant resonances of Ba, La and the lantha- nides have attracted great interest [ l and references therein]. The elements Ba, La and Ce occupy key positions for the understanding of these resonances, because the
"collapse" of the 4f orbital is expected to occur in this Z range [ I - 3 1 . Our photoelectron spectra of atomic Ba, La and Ce give detailed information on the final states and therefore on the character of the 4d giant resonances.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987989
C9-540 JOURNAL DE PHYSIQUE
Experiment
As a light source synchrotron radiation emitted by the storage rings BESSY and DORIS was used. The radiation was monochromatized by toroidal grating monochromators (E/AE
=300
...
800). For the photoelectron spectra the photon beam crossed an atomic beam emanating from a furnace heated by electron bombardment. The kinetic energy of the photo- and Auger electrons was determined by a cylindrical mirror analyzer (E/AE=135). For the photoabsorption measurements the atomic metals were maintained inside a resistance heated tubular furnace. The spectra were recorded photoelectrically.
Therefore our data are more reliable than earlier results obtained photographically.
binding
energy (eV)
Figure 1: Photoelectron spectra of atomic Ba, La and Ce taken at various photon energies.
gies at and above the giant resonance. The Ba 4d-I and
sp-'
photoelectron lines are split by spin-orbit interaction and accompanied by prominent satellite lines. In the case of La and Ce the more complicate multiplett splitting of the photoelectron and Auger lines is due to the open 5d and 4f shell. The background in the photoelectron spectra can be explained by electron emission arising from shake-off processes, which lead to multicharged ions in the final state.Figure 2:
photon energy ( e V )
top: La photoabsorption cross section, experiment (....), LDRPA (-)
[6] and HS calculation (-.-.-) [ 7 ] , in comparison to the sum of all partial photoionization cross sections ( 0 0 0 ) . The bars indicate the 4d-I ionization limits (Fig. 1).
center: 4d-I partial cross section of La, direct detection ( 0 0 4 ) ,
indirect detection via Auger ( * b e , CFS:.. ...), LDRPA ( ) [6] and RTDLDA calculation (---) [Zangwill, Dooton, unpublished].
-
1bottom: Experimental 5s-I (a,,), 5p ( o m , CIS: ....,) and (5d,6s)-'
(mom) partial cross section of La and corresponding LDRPA ( ) [6]
and RTDLDA calculations (---) [Zangwill, Dooton, unpublished]
C9-542 JOURNAL DE PHYSIQUE
As an example the absorption and various partial photoionization cross sections of atomic La are presented in Fig. 2. Calculated cross sections are included for compa-
10 9 9
rison. In agreement with theory the 4d +4d (4f,cf)+4d cf photoionization (4d-I) accounts for most of the absorption cross section. The resonance profile resembles the 4d shape resonance of atomic Xe and Cs [4-51. The 5p-1, 5s-', (5d6s)-l ioniza- tion channels are all resonantly enhanced. These partial cross sections, which in- clude the main lines and all satellites (Fig. l), display almost symmetric profiles centered at = 116.5 eV markedly below the position of the maximum of the 4d-I cross section. The absorption and the 4d-I cross section are well described by the LDRPA calculations. For the 5p-1 and 5s-I ionization channels the theory underestimates the cross sections at resonance by a factor of = 2.
The authors thank the BESSY staff for continued assistance. The financial support by the Bundesministerium fiir Forschung und Technologie is gratefully acknowledges.
[I] Giant Resonances in Atoms, Molecules an.d Solids, ed. by J.P. Connerade, J.M. Esteva and R.C. Karnatak, Plenum Press, New York (1987)
[2] K.T. Cheng and C. Froese-Fischer, Phys. Rev.
e,
2811 (1983) [3] K.T. Cheng and W.R. Johnson, Phys. Rev.g ,
2820 (1983)[4] U. Becker, Th. Prescher, E. Schmidt, B. Sonntag and H.E. Wetzel, Phys. Rev.
E ,
3891 (1986)[5] Th. Prescher, M. Richtsr, E. Schmidt, B. Sonntag and H.E. Wetzel, J. Phys.
B19, 1645 (1986)
[6] C ~ e n d i n , Lecture Notes for the Summer School "New Trends in Atomic Physics", Les Houches (1982)
[7] J.L. Dehmer and A.F. Starace, Phys. Rev.
