Photon Factory Activity Report 2004 #22 Part B (2005)
Atomic and Molecular Science

20A/2003G160

High-resolution threshold photoelectron study of the Kr 4s satellite states
Hiroshi YOSHII1*, Tomohiro AOTO2, Yumio MORIOKA3 and Tatsuji HAYAISHI4
1
Faculty of Medical Science, University of Fukui, Matsuoka, Fukui 910-1193, Japan2
Photon Factory, Institute of Materials Structure Science, Tsukuba, Ibaraki 305-0801, Japan
3
Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8571 Japan
4
Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, JapanExperiment
The experiments were performed on the beamline 20Aof the Photon Factory. The experimental set-up andtechnique were same as our previous study[3]. In brief,
photoelectrons extracted by a penetrating field werefocused by a lens system and then led to a hemisphericalelectrostatic analyser. In the spectrum recorded theFWHM for ionization of the 4s shell was ~7meV.
Results and Discussion
A part of the observed threshold photoelectron
spectrum at higher photon energy region is shown in Fig.
1. Rich satellite structures, 178 peaks including 48 newly
observed peaks, were found in our whole spectrum.
Although the feature of the observed spectrum is similar
to the previous threshold photoelectron spectrum [2]except for the improved peak width, it is different fromthe previous photoelectron spectrum [1]. Although manylines measured in this study were assigned by comparison
with the optically obtained energy levels [4], some ofthem could not be assigned.
In our spectrum, four Rydberg series were found. Oneis converging to the Kr2+ 3P2 state and the others to theKr2+ 1D2 state. The Rydberg series converging to the Kr2+3
P2 state was observed for the first time. This series hadbeen hard to observe, because high-n levels are hiding
behind a strong peak at 38.290 eV, the (1D)8s’ 2D5/2,3/2 state,
and low-n levels overlap with the other levels. Owing tohigh-resolution, eight energy levels of the Rydberg series
are separated in the present measurement between 38 and38.3 eV region.
Generally, the energy levels of the Rydberg series
could be expressed as following:
En=Elimit - RZ2/(n- )2,(1)where R, Elimit, Z and
are the Rydberg constant
employing the reduced mass of Kr, the converging limit,

the electric charge of the core ion, and the quantum defect,respectively. Since the observed eight levels belonging to
the newly observed Rydberg series satisfy this formulavery well, fitting the observed energy levels to thisformula was performed. The converging limit, Elimit,
obtained as the fitting result was 38.355 eV and it is inexcellent agreement with the energy level of the Kr2+ 3P2
state observed by a photoelectron-photoelectron
coincidence measurement [5], 38.36 eV. There are (3P)7p,(3P)8p and (3P)9p states observed by Alitalo et al. [1] near
low-n Rydberg levels predicted by the fitting. ThisRydberg series are , therefore, assigned to the (3P)npseries.
Three Rydberg series converging to the Kr2+ 1D2 state
were assigned to the (1D)nd’ 2D3/2, (1D)nd’ 2D5/2 and(1D)ns’ 2D5/2,3/2 series. The converging limit, Elimit, obtained
as the fitting result for the (1D)nd’ 2D3/2 series was 40.180
eV and it is in complete agreement with the Kr2+ 1D2 stateenergyobservedbyphotoelectron-photoelectron
coincidence measurement [5], 40.18 eV.
observed levels
predicted levels

Electron Yield (arb. unit)

Introduction
In the photoelectron spectrum of Kr, photoionization of
4s electron is accompanied with rich satellite structure,+
which corresponds to excited states of Kr , due to strong
electron correlations.
Recently, high-resolution photoelectron and thresholdphotoelectron spectra were measured [1, 2]. Full width at
half maximum (FWHM) of the observed peaks were ~27
meV and ~13 meV, respectively.
In the present study, a high-resolution thresholdphotoelectron spectrum of Kr, of which FWHM was ~7meV, was measured in the photon energy region between
the Kr+ 4s-1 main line and the Kr2+ 1D2 state.

7p?

3( P)7p

Ref. [1]8p?

9p?

3( P)9p( P)8p

15p

Kr2+ 3P2

3×4

35.5

36.0

36.5

37.0

37.5

38.0

38.5

Photon energy (eV)Fig. 1 A part of the observed threshold photoelectron spectrum

References[1] S. Alitalo et al., J. Electron Spectrosc. Relat. Phenom.
114-116, 141 (2001)[2] A. E. Slattery et al., J. Phys. B 33, 4833 (2000)[3] Yoshii et al., J. Mol. Specrosc. 186 155 (1997)[4] C. E. Moore “Atomic Energy Levels (NBS Circular)
vol. 2” (Washington, DC: US Govt Printing Office 1952)[5] R. I. Hall et al., J. Phys. B 25, 799 (1992)*yoshii@fmsrsa.fukui-med.ac.jp

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