Photon Factory Activity Report 2005 #23 Part B (2006)
Atomic and Molecular Science

2C/2005G087

Resonant Raman scattering in 1s-shell photoionization of O2 molecules

1
Tatsuji HAYAISHI*1, Satoshi IIZUKA1, Hisako YOSHIDA, Kaori YAMASHITA1,
4
Eigoro MURAKAMI3, Jun-ichi ADACHI and Akira YAGISHITA4
1
Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
2
Faculty of Medical Science, University of Fukui, Matsuoka, Fukui 910-1193, Japan3
Department of Physics, Chiba Institute of Technology, Narashino, Chiba 275-0023, Japan
4
KEK-PF, Tsukuba, Ibaraki 305-0801, JapanIntroduction
Doubly charged ions or more are observed in innershell photoionization of atoms. However, singly charged
ions in 1s-shell photoionization of Ne have been observedby means of coincidence spectroscopy with ions andthreshold photoelectrons [1]. Normally, Auger decays
following inner-shell photoionization result in theformation of doubly charged ions or more. On other hand,radiative decays instead of Auger decays take part in theformation of singly charged ions. Namely, the decay
process can be expressed as follows,+hν1 + M → M + e (threshold) + hν2 .
This process is the so-called continuous radiative resonant
Raman scattering [2].
In inner-shell photoionization of N2 molecules, singly
charged ions, that is parent ions of molecules, have been
also observed in coincidence with thresholdphotoelectrons [3]. The spectral structure was revealed by
the radiative decays.
Experimental method
Experiments were carried out at the undulator beamline
BL-2C. The beam line is equipped with a grazing
incidence soft X-ray monochromator. A varied spaceplane grating with 1000 lines/mm was used. The spectral
resolution of the monochromator with 50µ × 10µ slits was
about 0.15 eV at 550 eV photon energy. Multiply charged
ions in coincidence with threshold electrons weremeasured using a time-of-flight mass spectrometercoupled with a threshold-electron energy analyzer. Theenergy resolution of the analyzer was estimated to beabout 0.03 eV.
Results and discussion
Figure1 shows the yield spectra of ions, threshold+++++++photoelectrons and O2 , O and (O + O ) ions incoincidence with threshold photoelectrons near the 1sshell photoionization region of O2 molecules. The total
yield spectrum of ions is correspond to thephotoabsorption spectrum, and exhibits some resonancepeaks of 1s-shell photoexcitaion. The yield spectra ofthreshold photoelectrons and ions in coincidence with thethreshold photoelectrons exhibit broad and distorted
profiles due to post-collision interaction [4] in the 1s-shell
photoionization threshold, in addition to some resonance+peaks. However, the profile of parent ions O2 hassymmetry just in the ionization threshold. Therefore, the6Users' Reportformation of parent ions is due to continuous radiativeresonant Raman scattering [2].

Figure1. Yield spectra of ions, threshold electrons andions in coincidence with threshold electrons near the 1sshell photoionization region of O2 molecules.
References[1] E. Murakami et al., PF Activity Rep. 20, B, 12 (2002).
[2] T. Åberg and B. Crasemann, “Resonant anomalous Xray scattering” pp. 431-448 (Elsevier Science) (1994).
[3] T. Hayaishi et al., PF Activity Rep. 22, B, 2 (2004).
[4] T. Hayaishi et al., J. Phys. B. 27, L115 (1994).
*hayaishi@bukko.bk.tsukuba.ac.jp