Photoionization of Sc2+ ions by synchrotron radiation: Highresolution measurements and absolute cross sections in the photon energyrange 23-68 eV Page: 1 of 18
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Phys. Rev. A, submitted
Photoionization of Sc2+ ions by synchrotron radiation: High resolution measurements
and absolute cross sections in the photon energy range 23-68 eV
S. Schippers,i'* A. Muller,1 S. Ricz,2 M. E. Bannister,3 G. H. Dunn,4 A. S. Schlachterj G.
Hinojosa,6 C. Cisneros,6 A. Aguilar,? A. M. Covington,? M. F. Gharaibeh,7 and R. A. Phaneuf7
llnstitut fur Kernphysik, Justus-Liebig- Universitat, 35392 Giessen, Germanyt
institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), H-4001 Debrecen, Hungary
3Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
4JILA, University of Colorado, Boulder, Colorado 80309-0440
5Lawrence Berkeley National Laboratory, Advanced Light Source, Berkeley, California 94720
6Centro de Ciencias Fisicas, Universidad Nacional Autdnoma de Mexico,
Apartado Postal 6-96, Cuernavaca 62131, Mexico
?Department of Physics, University of Nevada, Reno, Nevada 89557$
(Dated: September 30, 2002)
Cross sections for the photoionization (PI) of Sc2+ ions with [Ar] 3d ground state configuration have
been measured by employing the merged ion-photon beams method. The Sc2+ ions were produced
from metallic vapor in an electron cyclotron resonance (ECR) ion source, and the photon beam was
generated by an undulator in the electron-synchrotron storage-ring of the Advanced Light Source
(ALS) of the the Lawrence Berkeley Laboratory. The experimental photon energy range 23 68 eV
encompasses the direct 3d and 3p photoionization thresholds. The experimental photo-ion spectrum
is dominated by autoionizing resonances due to 3p excitations predominantly decaying via Coster-
Kronig and Super-Coster-Kronig transitions. Individual resonances located around E ~ 40.2 eV
have been measured with an instrumental energy spread AE as low as 1.2 meV, corresponding to a
resolving power of E/(AE) around 33 500. The fractions of metastable ions in the Sc2+ ion beam are
obtained by comparing the photoionization cross section with the recently measured [Schippers et al,
Phys. Rev. A 65, 042723 (2002)] cross section for the time-reversed process of photorecombination
(PR) of Sc3+ ions. Absolute strengths of several 3p53d2 and 3p53d4s PI resonances have been
determined. They are the same as the corresponding resonance strengths for iso-electronic Ca+
ions.
PACS numbers: 32.80.Fb, 32.80.Hd, 34.80LxI. INTRODUCTION
Doubly charged scandium with its [Ar]3d ground state
configuration is the simplest atomic system with an open
3d shell [1]. It is even simpler than neutral scandium
which, in addition, to the 3d electron, has a closed 4s2
shell outside the argon core. Therefore photoionization
(PI) of Sc2+ is fundamentally interesting, especially in
view of the severe discrepancies between experimental [2]
and theoretical [3, 4] PI cross sections for neutral scan-
dium in the region of 3p -> 3d excitations. Likewise,
PI measurements with other, more complex transition
metal atoms and ions [5, 6] revealed large deviations of
the available theoretical results from the experimental
ones. These discrepancies are due to the fact that an ex-
act theoretical description of atomic systems with open
3p and 3d shells is extremely demanding and still be-
yond the capabilities of state-of-the-art atomic structure
calculations. Nevertheless, because of the scarcity of ex-
perimental PI data for atomic ions, theoretically derived
*Electronic mail: Stefan.E.Schippers strz.uni-giessen.de
tElectronic address: http://www .strz uni-giessen .de/"k3
tElectronic address: http://www.physics.unr.edu/facility/
pirf/pirf .htmlcross sections have to be relied upon, e. g., in the model-
ing of astrophysical or man-made plasmas. In response
to this unsatisfying situation one of the objectives of the
present study is to provide a benchmark for theoretical
PI cross sections of complex ions.
Photoionization of Sc2+ via 3p -> 3d excitations can
be represented ash + Sc2+(3s23p63d)
Sc2+(3s23p53d2)
Sc3+(3s23p6) + e-.(1)
The vertical arrow represents the intermediate doubly ex-
cited 3p53d2 states decaying predominantly by autoion-
ization via Super-Coster-Kronig transitions, and the di-
agonal arrow represents the direct 3d PI channel. It is
also possible to study the time reversed process of Eq. 1,
i. e. the photorecombination (PR) of a Sc3+(3p6) ion with
a free electron (e-). In PR the resonant and direct chan-
nels are termed dielectronic recombination (DR) and ra-
diative recombination (RR), respectively.
Theoretically, on a state-to-state level, PI and PR cross
sections are linked via the principle of detailed balance.
In a preceding publication [7] we have used the principle
of detailed balance to compare the present experimental
Sc2+ PI cross sections with measured Sc3+ PR cross sec-
tions [8]. It was shown that the study of both processes
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Schippers, Stefan E.; Müller, A.; Ricz, S.; Bannister, M. E.; Dunn, G. H.; Schlachter, A. S. et al. Photoionization of Sc2+ ions by synchrotron radiation: Highresolution measurements and absolute cross sections in the photon energyrange 23-68 eV, article, October 7, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc890650/m1/1/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.