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

NE1B/2004G201

Multi-Electron Coincidence Study on Auger Decay
from Ne 1s Photoionization Satellites
Yasumasa HIKOSAKA1, Tomohiro AOTO2, Pascal LABLANQUIE3, Francis PENENT3,
Eiji SHIGEMASA1, Kenji ITO2
1
UVSOR, Institute for Molecular Science, Okazaki 444-8585, Japan
2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
3
Laboratoire de Chimie Physique-Matière et Rayonnement, 75231 Paris Cedex 05, Francesatellites undergo Auger decay processes differing+-1
markedly from the Ne 1s decay.
+-1-1
The first Auger decay from the Ne 1s 2p np satellite
states does not yield such slow electrons in the 0-25 eV
2+range, because no Ne state is expected in the ionization+-1-1
range lying 0-25eV below the Ne 1s 2p np states.
Therefore, these slow electrons with discrete energies
result from the subsequent decay of states created by thefirst Auger decay. In practice, we observe the first Auger
electrons in the triple coincidence events including thesatellite photoelectrons and the slow electrons. Based on
the energy correlations between the two Auger electrons,
2+3+
we have assigned the intermediate Ne and final Nestates [3].
Electron energy (eV)(a)
203040-15060

1s 2p ( P)np4 3
1P 3
4 3
P5000

80-11s810000

70-1 1,3

8Counts15000(b)
Kinetic energy of slow electron (eV)Introduction
The removal of a core electron may be accompanied by
the promotion of a valence electron to a vacant orbital.
The photoionization satellite states will proceed bycharacteristic Auger decays and then produce specificmultiply-charged ion states, because the decays reflect
their outer electron configurations differing from the main
core-hole states. The investigation of the decay processesof the satellite states has been very limited so far, because
the cross sections for the formation of the satellite states
are unfavorable and the corresponding Auger events areeasily hidden behind the events associated with ordinary
core-hole photoionization.
In this work we have investigated the Auger decay of
Ne 1s photoionization satellite states. We have used amagnetic bottle type electron spectrometer whose
powerful capability in electron coincidence observations
has recently been described [1,2]. The coincidence dataset
includes complete information on the energy correlations
among the multi-electrons emitted, from which we havededuced the Auger decay mechanism from the 1s
photoelectron satellite states.
Results and Discussion
A multi-electron coincidence dataset was accumulated
for Ne at the excess energy of 77.8 eV above the Ne 1s
ionization threshold at 870.09 eV. Fig. 1(a) shows aphotoelectron spectrum, where the energy range isarranged to show the photoelectron peaks for the+-1formations of the Ne 1s state and the satellite states. The+-1-1 1,3
photoionization satellite states, Ne 1s 2p ( P)np, areresolved only partially in Fig. 1(a) with the instrumental
resolution of about 1 eV. Fig. 1(b) displays coincidences
between the photoelectron lines from Fig. 1(a) and slow
electrons in the 0-30 eV kinetic energy range. On the twodimensional map a striking difference can be seen
between the slow electron distributions in coincidences+-1with the Ne 1s and satellite photoelectrons. The slow
electron distribution in coincidence with the 1s
photoelectrons shows a monotonic decrease withincreasing slow-electron energy. The slow electrons incoincidence with the 1s photoelectrons are slower Auger+electrons in the direct double Auger decay from the Ne-1
1s state. In contrast, knots of enhancements are observedin the 0-25 eV range for the slow electron distributions
measured in coincidence with the satellite photoelectrons.
The structured slow electron distributions indicate that the030252020015150
10100
550
0020304050607080

Kinetic energy of fast electron (eV)Fig. 1 (a) Inner-shell photoelectron spectrum of Ne
measured at a photon energy of 947.9 eV. (b) Two
dimensional map of all coincidence yields, represented asa function of the kinetic energies of fast and slow
electrons. Coincidence counts are plotted on a linear scale.
References[1] J.H.D. Eland et al., Phys. Rev. Lett. 90, 053003(2003).
[2] F. Penent et al., Phys. Rev. Lett. 95, 083002 (2005)[3] Y. Hikosaka et al., J. Phys. B, submitted.
hikosaka@ims.ac.jp

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