EGAS41 - Swansea University

41 st EGAS CP 154 Gdańsk 2009
Lineshapes of even Ar(np ′ , nf ′ , J = 0, 1, 2) autoionization spectra
excited from selected low-lying odd excited J = 1 levels
U.Hollenstein 1 ,L.J.Kaufmann 1 ,F.Merkt 1 ,I.D.Petrov 2,3 ,V.L.Sukhorukov 2,3 ,H. Hotop 3,∗
1 Laboratorium für Physikalische Chemie, ETH Zürich, CH - 8093 Zürich, Switzerland
2 Rostov State University of Transport Communications , Rostov-on-Don 344038, Russia
3 Fachbereich Physik, Techn. Univ. Kaiserslautern, D-67653 Kaiserslautern, Germany
∗ Corresponding author: hotop@physik.uni-kl.de
Recent laser photoionization studies yielded the first results for the lineshapes of the even
Ne(np ′ ) autoionizing Rydberg states (ARS), as excited from the metastable Ne(3s 3 P 2 , 3s ′
3 P 0 ) [1] and from the short-lived Ne(3s, 3 P 1 , 3s ′ , 1 P 1 ) levels [2]. Configuration interaction
Paul-Fock including core polarization (CIPF CP) calculations of the Ne(np ′ ) spectra
yielded good overall agreement with the shapes, widths and energy positions of the measured
resonances [1,2]. However, a proper theoretical description of the Ne(np ′ [1/2] 0 ) resonances,
especially the strong differences between the spectra, excited from the two J = 1
levels, turned out to be demanding [2]. These differences were found to be the result of the
interference between the direct 〈3s|r|np〉 and the intershell 〈3s|r|3p〉〈3p|V (2p 2p)|np〉 amplitudes
which is constructive in the 3s ′ → np ′ transition and destructive in the 3s → np ′
transition. Calculations of the np ′ spectra of the heavier rare gas atoms exhibit trends
which clearly reflect the influence of the rising spin-orbit splitting of the ion core [3].
A very recent two-color photoionization experiment on Ar by Lee et al. [4], combining
excitation of ground state Ar atoms to several low-lying odd parity (ms, md) J = 1
levels (especially 7s ′ [1/2] 1 and 8s[3/2] 1 ) by monochromatized synchrotron radiation with
subsequent laser excitation to Ar(np ′ , nf ′ ) resonances raised questions on the validity
of our theoretical predictions, especially for the different lineshapes of the Ar(np ′ , J =
0) resonances. To shed further light on this problem, we carried out a new two-step
excitation experiment, using the pulsed Zürich atomic beam setup. The three excited
levels Ar(4s ′ [1/2] 1 , 3d[1/2] 1 , 5s[3/2] 1 ) were prepared from the Ar ground state by a pulsed
XUV laser source [5] (width 12 GHz) and further excited by Fourier-transform limited UV
laser (width 100 MHz), perpendicular to the XUV beam. The UV laser was continuously
tuned to record the Ar(np ′ , nf ′ ) autoionization spectra of interest. The linear polarization
vectors of both light beams could be chosen parallel or perpendicular to each other. An
observation of particular interest, presenting a challenge to theory, is the near-absence
of the np ′ , J = 1, 2 resonances (n around 15) in the ARS spectra excited from the
Ar(4s ′ [1/2] 1 ) level.
At the conference we shall compare the experimental spectra from both the previous
[4] and the Zürich experiments with our most advanced calculations.
Acknowledgment
Support by the Swiss National Science Foundation and by the Deutsche Forschungsgemeinschaft
(Ho427/30) is gratefully acknowledged.
References
[1] T. Peters et al., J. Phys. B 38, S51 (2005)
[2] I.D. Petrov et al., J. Phys. B. 39, 3159 (2006)
[3] I.D. Petrov et al., Eur. Phys. J. D 40, 181 (2006)
[4] Y.Y. Lee et al., Phys. Rev. A 78, 022509 (2008)
[5] U. Hollenstein et al., Rev. Sci. Instrum. 71, 4023 (2000)
214