Ⅲ-3
Atoms and
Molecules

Ⅲ -3. Atoms and Molecules

BL3U

In-Situ Observation of Electrochemical Reaction by Soft X-Ray Absorption
Spectroscopy with Potential Modulation Method
M. Nagasaka, H. Yuzawa, T. Horigome and N. Kosugi

Institute for Molecular Science, Myodaiji, Okazaki 444-8585, JapanFor understanding the electrochemical reaction, it
is most important to investigate local structures ofelectrolytes including electric double layers at
different
potentials.
Soft X-ray
absorption
spectroscopy (XAS) is an element specific method tostudy local electronic structures of solutions andinterfaces. Recently, we developed a liquid cell for
XAS in transmission mode [1], in which the thicknessof the liquid layer is controllable between 20 and2000 nm. In addition, we successfully measured XASof electrolytes in electrochemical reaction by using aliquid cell with built-in electrodes [2]. From the Fe
L-edge XAS spectra of aqueous iron sulfate solutions
in electrochemical reaction, we revealed change inthe valence of Fe ions at different potentials, where
each XAS spectrum was measured at a constantpotential and the scanning rate of the potential (0.08mV/s) was quite slower than that in regular cyclic
voltammetry (CV) (typically 100 mV/s). In this study,
we have developed a potential modulation method tomake possible in-situ XAS observation ofelectrochemical reaction at the same scanning rate ofCV.
In the XAS measurement with a potential
modulation method, the electrode potential is swept at
a fixed photon energy, and soft X-ray absorption
coefficients at different potentials are measured at thesame time. After repeating the potential modulation at
different photon energies, we can get XAS ofelectrolytes in electrochemical reaction at the samescanning rate of CV.
The experiments were performed at BL3U. XAS
spectra of electrolytes were measured by using aliquid cell with built-in electrodes [2]. Figure 1 shows
the Fe L-edge XAS spectra of aqueous iron sulfate
solutions in electrochemical reaction at 100 mV/s. By
increasing the potential from 0.0 to 1.0 V, the peakintensity of Fe(II) (708 eV) is decreased and that ofFe(III) (710 eV) is increased by the oxidation of
Fe(II). By decreasing the potential from 1.0 to -0.4 V,
the peak intensity of Fe(II) is increased, and that ofFe(III) is instead decreased by the reduction of
Fe(III).
To obtain the fraction of Fe(II) and Fe(III) ions, theFe L-edge XAS spectra at different potentials are
fitted by superposition of the reference XAS spectraof Fe(II) and Fe(III) ions. Figure 2 shows fractions ofFe(II) and Fe(III) ions in electrochemical reaction at
100 mV/s. By increasing the potential, the fraction of
Fe(III) is increased and that of Fe(II) is decreased.

109

The Fe(II) ions are partially changed to the Fe(III)ions by the oxidation process. It is because a thickliquid layer is necessary for XAS of dilute Fe ions intransmission mode. As shown in the inset of Fig. 2,
the XAS spectra includes both the solid-liquidinterface that occurs the Fe redox reaction and thebulk electrolyte of Fe(II) that does not involve theelectrochemical reaction. The mechanism of these Fe
redox process will be discussed by correlating the
XAS results with those at the different scanning rates.

Ⅲ-3

Fig. 1. Two dimensional plots, photon energy andpotential (versus Ag/AgCl), of the Fe L-edge XAS
spectra in electrochemical reaction of aqueous ironsulfate solutions at the scanning rate of 100 mV/s.

Fig. 2. Fractions of Fe(II) and Fe(III) ions as afunction of potential (versus Ag/AgCl) in
electrochemical reaction at 100 mV/s. The inset
shows a partial oxidation model in a liquid cell.
[1] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.
[2] M. Nagasaka et al., J. Phys. Chem. C 117 (2013)
16343.

Ⅲ -3. Atoms and Molecules

BL3U

Interaction of Pyridine with Water in Aqueous Solution Studied by SoftX-Ray Absorption Spectroscopy in C and N K-edges
M. Nagasaka, H. Yuzawa and N. Kosugi

Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan

Ⅲ-3

Pyridine is liquid and is soluble in water at any
concentration. In aqueous pyridine solution, theformation of hydrogen bond (HB) between the N siteof pyridine and the H site of water is proposed by thevibrational spectroscopy [1]. But the local structure ofpyridine-water mixture is unknown. Soft X-ray
absorption spectroscopy (XAS) is an element specificmethod applicable to the local structure study. In thepresent work, we have measured the C and N K-edge
XAS of pyridine-water mixtures at different
concentrations, and investigated the interaction of the
C and N sites of pyridine with water in the binary
solutions.
The experiments were performed at BL3U. XAS ofliquid samples were measured by a transmitted-type
liquid cell at 25 °C [2]. The liquid layer was
sandwiched between two 100 nm-thick Si3N4
membranes. The thickness of the liquid layer iscontrollable between 20 and 2000 nm by adjusting
the He backpressure.
Figure 1(a) shows the C K-edge XAS of pyridine
gas and pyridine-water solution (C5H5N)X(H2O)1-X.
The transition C 1s ! "* shows two peaks: First peak(C1) is derived from the meta- and para-C sites ofpyridine. The second peak (C2) is the ortho-C sites.
From gas to liquid pyridine (X=1.0), both the C1 andC2 peaks are shifted to the lower photon energy.
Figure 1(b) shows the N K-edge XAS of pyridine gas
and pyridine-water solutions. The N 1s ! "* peakshows the higher energy shift from gas to liquid.
These energy shifts are consistent with those of thepyridine clusters with an antiparallel structure [3], but
are smaller than in the cluster case.
By increasing the molar fraction of water inpyridine-water solution, the XAS peaks are shifted asshown in Fig. 1. Table 1 shows the peak shifts ofpyridine-water mixtures from that of liquid pyridine.
The C1 peaks related to the meta- and para-C sites
are not changed at different concentrations. The C2
peaks related to the ortho-C sites are slightly shiftedto the higher photon energy by increasing the molar
fraction of water. The N peaks are more evidently
shifted to the higher photon energy. These energy
shifts are reasonable, assuming that the energy shiftarises from HB between the N site of pyridine andwater in the pyridine-water binary solutions. The
order of the magnitude of the peak energy shift (N >C2 > C1) is caused by weakening the influence of HBinteraction of water at each site of pyridine withfather from the N site of pyridine.

Fig. 1. XAS spectra of pyridine-water mixtures atdifferent concentrations in (a) C and (b) N K-edges.
The XAS spectra of pyridine gas are also shown. The
peaks are shifted to the direction of arrows by
increasing the molar fraction of water.
Table 1. Peak energy shifts (eV) of pyridine-water
mixtures from liquid pyridine (X=1.0).
(C5H5N)X(H2O)1-X
C1
C2
N
Gas
0.10
0.04
-0.08
X=1.0
–
–
–
X=0.8
0.00
0.01
0.04
X=0.5
-0.02
0.02
0.08
X=0.3
-0.02
0.02
0.10
X=0.05
-0.02
0.05
0.14
[1] S. Schlücker et al., J. Phys. Chem. A 105 (2001)
9983.
[2] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.
[3] I. L. Bradeanu et al., J. Phys. Chem. A 112 (2008)
9192.

110

Ⅲ -3. Atoms and Molecules

BL3U

Soft X-Ray Absorption Spectroscopic Study of Solid-Liquid Interface
H. Yuzawa, M. Nagasaka and N. Kosugi

Institute for Molecular Science, Okazaki 444-8585, Japan
Detailed understanding of the interface interaction
is important to clarify physical and chemical
phenomena such as molecular adsorptions, catalytic
reactions and so on. However, the solid/liquidinterface is difficult to measure because it involves
two different condensed phases. We generally use
particle (electron, ion etc.) or light (IR, X-ray etc.)
probe to investigate geometric and electronic
structures, but the former interacts too strong withboth phases to observe the interface. The latter only
gives average information of the interface and bulk,
where the information of the interface (minor
component) get covered up by that of the bulk [1].
Thus, new approaches are required to measure thesolid/liquid interface.
We developed a transmission-type liquid XAS(X-ray Absorption Spectroscopy) cell with Si3N4 or
SiC windows, which is able to control easily the
thickness of the liquid thin layer (20-2000 nm), forthe soft X-rays [2]. From the other point of view, thisliquid cell contains solid/liquid interfaces and canstrengthen the information of the interface for lightprobe by controlling the liquid thickness. Thus, we
tried to detect the interaction of solid/liquid interface
in the liquid XAS cell, whose surface is modified toobjective structures.
The experiments were carried out in BL3U. Two
Au (thickness: 20 nm) and Cr (5 nm) deposited Si3N4(100 nm) membranes were used as liquid cell
windows. The model surface in this study was
prepared by the modification (chemisorption) of 1H,
1H, 2H, 2H -perfluorodecanethiol (F-thiol)monolayer on the gold surface (Fig. 1).

Au

F F F F F FFF F F F F F F F

F
F

Au
Au

S

FF

2

S

7

F
F

7

F
FF

FF F

2

Au deposited film
Soft X-ray
Liquid(H2O or PhH)

F-thiol monolayer
Si3N4 membrane

Detector
Teflon sheet

Fig. 2. Schematic (side view) of soft X-ray XAS
measurement to detect the interaction at thesolid/liquid interface.

Intensity / a.u.

Au
+ 2 HSOn the other hand, when the absorption peak (285.1
eV, 1sπ*) of benzene (green line) extracted fromthe red line was compared with that without the liquidcell modification of F-thiol (black line), the width of
the absorption peak broadened. This would be
because the electronic state of benzene molecule was
influenced by the interactions between the F atom in
F-thiol and the benzene molecule at the interface, e.g.,-FH- interaction [3] and -Fπ interaction [4].
Thus, the trace of the interface interaction could be
detected in the liquid side.
Through the above experiments, we can conclude
that the transmission soft X-ray XAS approach has apotential to detect the interaction of solid/liquidinterface.

+ H2

285

Fig. 1. Modification of gold surface by F-thiolmonolayer.

290
295
300
Photon Energy / eV

305

Fig. 3. C K-edge XAS spectra of the modified liquidcell filled with water (blue line) or benzene (red line)
and that of the unmodified one filled with benzene(black line). Green line corresponds to the spectrumof the red line subtracted by that of the blue line toremove the influence of the absorption of F-thiol.

Then, the cell was filled with liquid (water or
benzene) and C K-edge XAS was measured at room
temperature as shown in Fig. 2.
Figure 3 shows the C K-edge XAS spectra of themodified liquid cell filled with water (blue line) or
benzene (red line). In both cases, three absorption
peaks (> 290 eV), which correspond to the excitationfrom C 1s to σ* of F-thiol, were observed. It was
confirmed that this system could detect the soft X-ray
absorption of molecule at the solid/liquid interface.
Nevertheless, the energy positions of each absorption
peak were consistent regardless of liquid phase.

[1] F. Zaera, Chem. Rev. 112 (2012) 2920.
[2] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.
[3] M. D. Prasanna et al., Cryst. Eng. 3 (2000) 135.
[4] B. Brammer et al., New J. Chem. 23 (1999) 965.

111

Ⅲ-3

Ⅲ -3. Atoms and Molecules

BL3U

Interaction of Acetonitrile with Water in Aqueous Solution Studied by SoftX-Ray Absorption Spectroscopy in C and N K-edges
M. Nagasaka, H. Yuzawa and N. Kosugi

Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan

Ⅲ-3

Acetonitrile is liquid and is soluble in water at any
molar fraction. In aqueous acetonitrile solution, twomodels of the acetonitrile-water dimer were proposed[1]: One is a hydrogen bond structure between the Nsite of acetonitrile and the H site of water. The otheris a dipole-bonded structure that water is parallel to
the C!N group of acetonitrile by the dipole
interaction. Huang et al. measured the O K-edge
X-ray absorption spectra (XAS) [2] and proposed thatthe dipole-bonded dimer is abundant compared to thehydrogen bond structure. However, the interaction
has not yet been studied from the acetonitrile side. In
this study, we have measured the C and N K-edge
XAS of acetonitrile-water solutions at different
concentrations, and revealed the interaction of the
C!N group of acetonitrile with water.
The experiments were performed at BL3U. XAS ofliquid samples were measured by a transmitted-type
liquid cell [3]. The liquid layer was sandwiched
between two 100 nm-thick Si3N4 membranes. The
thickness of the liquid layer is controllable between
20 and 2000 nm by adjusting the He backpressure.
Figure 1 shows the C and N K-edge XAS spectra ofacetonitrile gas and acetonitrile-water solution(CH3CN)X(H2O)1-X. From gas to liquid acetonitrile(X=1.0), both the C 1s " C!N #* and N 1s "C!N#* peaks are shifted to the higher photon energy. It isbecause liquid acetonitrile shows the antiparallel
structure between the C!N groups of acetonitrile by
the dipole interaction.
Table 1 shows the peak shifts of acetonitrile-water
mixtures from that of liquid acetonitrile. The C peakis shifted to the higher photon energy by increasing
the molar fraction of water. On the other hand, the N
peak is shifted to the lower photon energy. Theinteraction of the C site of the C!N group is increased
by water, and that of the N site is slightly decreased.
These results suggest that the acetonitrile-water
solution may have the dipole-bonded structure, inwhich the oxygen site of water is close to the C site of
the C!N group of acetonitrile. It should be also notedthat the peak width at X=0.05 is narrower than thoseat different molar fractions, suggesting that in dilute
aqueous solutions acetonitrile molecules may beisolated by the dipole interaction with watermolecules.

Fig. 1. XAS spectra of acetonitrile-water mixtures atdifferent concentrations in (a) C and (b) N K-edges.
The XAS spectra of acetonitrile gas are also shown.
The peaks are shifted to the direction of arrows by
increasing the molar fraction of water.
Table 1. Peak energy shifts (eV) of acetonitrile-water
mixtures from liquid acetonitrile (X=1.0).
(CH3CN)X(H2O)1-X
C
N
Gas
-0.09
-0.09
X=1.0
–
–
X=0.8
0.02
-0.02
X=0.5
0.02
-0.02
X=0.3
0.02
-0.03
X=0.050.05-0.03[1] I. Bakó, T. Megyes and G. Pálinkás, Chem. Phys.
316 (2005) 235.
[2] N. Huang et al., J. Chem. Phys. 135 (2011)
164509.
[3] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.

112

Ⅲ -3. Atoms and Molecules

BL3B, BL5B, BL7B

Absorption Measurement of Amino Acid Films Using a Novel in situ
Vacuum Sublimation System
K. Ishiyama, Y. Tanigawa, S. Takenaka and K. Nakagawa

Graduate school of Human Development and Environment, Kobe University, Kobe 657-8501, Japan
It was suggested by Platzman [1] that themagnitude of radiation effect by high energy particle
radiation is proportional toTd f dE∫ dE E ,0where, T the kinetic energy of particle, f the oscillator
strength and df/dE is the oscillator strength
distribution which is proportional to the absorption
cross section σ. Since T is sometimes order of MeV,
we need to measure σ(E) for 5 eV<E<1 MeV.
Synchrotron radiation is very powerful tool tomeasure such wide-energy-range absorption spectra.
One of difficulties to measure σ(E) within suchwide energy range is the large dynamic range ofσ (E). For example, for alanine film, σ (E=17eV)=1.2x10-16 cm2 and σ (E=250eV) =6.8x10-19 cm2 ; theratio is 5600. Thus in order to obtain the reliable
spectrum, we must change the film thickness over 20
times. In order to do this, we developed a novel insitu sublimation system (Fig. 1). Substrate is made ofKapton film with very small heat capacity, which is
helpful to prevent overheat. Wide area of substrate
allows us to get the high sublimation yield.
Figure 2 shows an example of absorption spectrumofglutamine measured at BL-5B. First wemeasured with the grating 2 and the mirror 4 (G2M4)
plus the aluminum filter. After that we changed themeasurement system to G2M4 and added thethickness of the same glutamine film to get the
spectrum designated by “G2M4”. Repeating thisprocedure, we obtained four spectra shown in Fig. 2.
Thickness of “G2M1” film was roughly estimated to
be about 4.5 times of “G2M4+Al” film.
Connecting four spectra in Fig. 2, we determinedthe experimental data as shown in Fig. 3.
Using the in situ sublimation system, we willcomplete the measurement of 20 amino acidmolecules, among which several spectra were alreadyreported [2].

Fig. 1. A novel in situ sublimation system.

Optical Density

0.6

L-Glu

G2M4

Ⅲ-3

0.4

G2M1

0.2

G2M4+Al

G2M2
0.0

0

5

10

15

20

25

30

35

40

45

Wavelength / nm

Fig. 2. Absorption spectra of glutamine measured
at BL5B.

Optical Density

0.8

G2M4+Al

L-Glu

0.7
0.6
0.5
0.4
0.3

G2M4

G2M2

0.2
0.1
0.0

G2M1
0

5

10

15

20

25

30

Wavelength / nm

35

40

45

Fig. 3. Determined experimental data.
[1] R. L. Platzman, Vortex, 23 (1962) 372.
[2] M. Kamohara, Y. Izumi, M. Tanaka, K. Okamoto,
M. Tanaka, F. Kaneko, Y. Kodama, T.Koketsu andK. Nakagawa, Rad. Phys. Chem. 77 (2008) 1153.

113

Ⅲ -3. Atoms and Molecules

BL4B

Multi-Electron-Ion Coincidence Spectroscopy by Using a Magnetic Bottle
Electron Spectrometer
I. Umekawa1, Y. Shibata1, K. Soejima1, E. Shigemasa2 and Y. Hikosaka1
1

Ⅲ-3

Department of Environmental Science, Niigata University, Niigata 950-2181, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

A doubly-charged molecular ion can be formed bydouble photoionization in which two electrons are
released from the molecule by absorbing a photonwith energy above the double ionization potential.
Such molecular dication states are inherently
dissociative due to the Coulomb repulsion between
the two positive charges, though the lifetimes aredifferent from the electron states and further from thevibrational levels. While the information of the
lifetimes is important in simulations of atmospherecompositions [1], experimental determinations of the
lifetimes depending on vibronic states are still limited
even for simple molecules.
In this work, we have developed an electron-ion
coincidence spectrometer, with an aim to investigate
the stabilities of individual vibronic states inmolecular dications. The coincidence spectrometer isbased on a magnetic-bottle time-of-flight electron
spectrometer [2], which schematic is shown in Fig. 1.
Electrons produced by photoionization of sample
molecules are collected by an inhomogeneous
magnetic field over 4! solid angle, and their kinetic
energies are determined from the times of flight to a
micro channel plate detector. At 10 µs later than theincidence of the photoionization light pulse, pulsed
high voltages are applied to the electrodes placed
across the photoionization region, which extracts theions staying in the ionization region toward the samedetector.
Figure 2 shows a time-of-flight spectrum measured
for CO2 at a photon energy of 59.7 eV, wheretimes-of-flight of electrons (ions) are observed before(after) 10 µs. In the spectrum, a weak peak for
double-charged CO22+ ions can be seen, in addition tomono-cation peaks. The observation of the CO22+ ionsis attributed to the formation of doubly-charged ion
states with lifetimes in the order of µs or longer;
otherwise, only the fragment ions should be observed
due to dissociation before reaching the detector.
In order to investigate the doubly-charged ion
states relevant to the metastable CO22+ ions, kinetic
energies of the electron pairs observed in coincidencewith the CO22+ ions are extracted. Figure 3 shows theenergy correlations of the electron pairs. Twophotoelectrons emitted on double photoionization
shares the available energy which is the energy
difference of the photon energy and the binding
energy of a formed doubly-charge ion state. Thus, theformation of a doubly-charge ion state appears on theenergy correlation map as a diagonal structure with aslope of -1. In practice, corresponding structures are

discernible on the map in Fig. 3 around (fasterelectron energy) + (slower electron energy) = 20 eV.
The binding energies of doubly-charge ion states
relevant to the metastable CO22+ are determined to 40
eV, which confirms a previous measurement [3]. We
plan further measurements, as detailed discussion
needs higher statistics in the coincidence data.

Fig. 1. Schematic of the electron-ion coincidence
spectrometer.

Fig. 2. Time-of-flight spectrum measured for CO2 at a
photon energy of 59.7 eV, where times-of-flight ofelectrons (ions) are observed before (after) 10 µs..

Fig. 3. Energy correlation between two photoelectron
observed in coincidence with metastable CO22+ ions.
[1] R. Thissen et al., Phys. Chem. Chem. Phys. 13(2011) 18264.
[2] A. Matsuda et al., Rev. Sci. Instrum. 82 (2011)
103105.
[3] A. E. Slattery et al., J. Chem. Phys. 122 (2005)
084317.

114

Ⅲ -3. Atoms and Molecules

BL6U

The Observation of Doppler Profile of Photoelectrons Emitted from
Rydberg Oxygen Atom Following O 1s Inner-Shell Excitation of CO2
T. Gejo1, K. Myojin1, T. Tajiri1, K. Maekawa1, K. Honma1, H. Iwayama2 and E. Shigemasa2
1

University of Hyogo, Ako-gun 678-1297, JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan115

those expected from the # value obtained by the angular
distribution of fragment ions, which is 0 ~ 1 at
excitation energies around 1s ionization threshold [1].
Thus, these relatively high # values suggest that theabsorption due to $ % $ transition is more importantrole on the generation of O* fragments than & % $transition. This can be rationalized by that np' type
Rydberg transition is much suitable to generate theseO*.

a)

Intensity / arb. units

Molecules following photo-excitation in the vicinityof inner-shell ionization thresholds provides interesting
properties. For photon energies just above ionizationthreshold, an electron can escape from the ion as a slow
photoelectron. The core-hole ion, however, immediately
undergoes Auger decay, emitting a fast Auger electron.
This leads to a drastic increase of the strength of the
Coulomb interaction between the slow out-going
photoelectron and the residual ion. When the slow
electron lose sufficient kinetic energy by this retardation,
it become recaptured by the molecular ion into a
Rydberg state. The recapture of the photoelectron
results in high-n Rydberg states in singly charged ion.
After that, the ion undergoes fragmentation. Since theelectron in Rydberg states are relatively stable, Rydberg
atom can be generated after this ion fragmentation. Thiscan be confirmed by photoelectron spectra in low
kinetic energy region, since Rydberg atom may emit theelectron by changing its ion core state.
We have investigated low energy photoelectron
spectra of CO2 in O 1s excited state region. Since twooxygen atom locate at ends of CO2, one can expect highkinetic energy of Rydberg oxygen atom (O*). As aresult, the photoelectron spectra due to O* is expected
to show splitting by strong Doppler effect, which gives
the information about dynamics of O* generation.
The experiment was performed on the soft X-ray
undulator beamline BL6U at UVSOR. To record theelectron kinetic energy spectra, we used ahemispherical electron energy analyzer (MBS1)
equipped with a gas cell. The resolution of the electron
analyzer was set to approximately 8 meV. The typicalpressure in the main chamber housing the gas cell was
about 1.0 ! 10"3 Pa during the measurements. The
polarization of the incident photon beam generated by
the undulator is horizontal and the photoelectron
analyzer can be rotated at horizontal or vertical position
respect to this polarization. Energy calibration of theincident photon beam was carried out by recording thetotal ion yield spectrum of CO2 in the vicinity of the O
1s ionization threshold.
Figure 1 shows the photoelectron spectra of CO2
obtained at photoexcitation energies of 538.85, 539.50,
539.90, and 540.65 eV. The peaks clearly show the
Doppler splittings, implying that O*s are generated topolarization direction. We have fitted the Doppler
profiles with assuming on Gaussian kinetic energy
distribution and one # parameter. The result of thefittings provides # ~ 1.2. These results show highpreference for parallel direction, which is more than   



2.4

2.6

2.8

3.0

3.2

3.4

Kinetic energy / eVb)

Intensity / arb. units2   



2.4

2.6

2.8

3.0

3.2

3.4

Kinetic energy / eV

Fig. 1. Photoelectron spectra of Rydberg oxygen
atom, following O 1s inner-shell excitation of CO2
The electron analyzer set at a) horizontal and b)
vertical position to polarization of SR, and theexcitation energies are 538.85, 539.50, 539.90, and540.65 eV .
[1] K. Okada et al., Phys. Rev. A, 66 (2002) 032503.

Ⅲ-3

Ⅲ -3. Atoms and Molecules

BL6U

Formation of H3+ Fragment Following Auger Decay in Ethane
Y. Shibata1, T. Shirota2, K. Hoshina2, H. Iwayama3, E. Shigemasa3 and Y. Hikosaka1
1

2

Ⅲ-3

Department of Environmental Science, Niigata University, Niigata 950-2181 Japan
Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences,
Niigata 956-8603 Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan

Formation of H3+ fragment ion has been widely
observed in the dissociations of organic molecular
dications. The mechanism of the H3+ formation has
absorbed special attention, in connection withrearrangements of the molecular structures due torapid hydrogen migration [1, 2]. In this work, wehave investigated the dication states relevant to theH3+ formation from C2H6 molecules, by using an
Auger electron-ion coincidence method.
The experiment was performed at the undulator
beamline BL6U, by using an Auger electron-ion
coincidence spectrometer consisting of a double
toroidal electron analyzer and a three-dimensional ion
momentum spectrometer [3-5]. Auger electronsejected at ~54.7º with respect to the electric vector of
the incident light were sampled and analyzed inenergy by the electron analyzer. According to thedetection of each Auger electron, a pulsed electricfield was applied to the interaction region, in order toextract the formed ions into an ion momentum
spectrometer.
The top panel of Fig. 1 shows a time-of-flight
spectrum of ions measured in coincidence with C1s
Augerelectrons
emittedafter
inner-shell
photoionization of C2H6 molecules. In this spectrum,fragment ion manifolds for the CHn+ and C2Hn+
sequences are observed around 1300 ns and 2000 ns,
respectively. Below 500 ns, besides the H2+ peak, aweak peak assignable to H3+ is discernible. The
bottom panel of Fig. 1 shows a two-dimensional map
for the correlations between fragment ions detected incoincidence with an Auger electron. Here, an area
covering coincidences between H3+ (vertical axis) andthe counterpart ions (horizontal axis) is presented. On
the two-dimensional map, clear structures forcoincidences between the fragment ion pairs of H3++C2H3+ and H3++ C2H4+ can be identified, while any
structure for the pairs of H3++ CHn+, accompanying
the C-C bond dissociation, is indiscernible.
Figure 2 shows a C 1s Auger spectrum filtered withthe detection of the H3++C2H3+ ion pair, comparedwith the total Auger spectrum. The total Auger
spectrum exhibits only a broad band structure
resulting from overlap of different dication states.
One finds that the formation of the H3++C2H3+ ion
pair is associated with low-lying dication states in thebinding energy range of 40-55 eV, and thedissociation of the states lying in this range result in
the formation of H3+ fragment. The dication stateswith the electronic configuration of 1eg-2 are known

to lie in this binding energy range [6].

Fig. 1. (Top) Time-of-flight spectrum of ions and(Bottom) two-dimensional map for the correlations
between fragment ions, both of which are measured
in coincidence with C1s Auger electrons emitted after
inner-shell photoionization of C2H6 molecules.

Fig. 2. C1s Auger spectrum of C2H6 (black), andcoincidence Auger spectrum filtered with theformation of the H3++C2H3+ ion pair (red).
[1] K. Hoshina et al., J. Chem. Phys. 134 (2011)064324.
[2] K. Hoshina et al., J. Chem. Phys. 129 (2008)
104302.
[3] T. Kaneyasu et al., AIP Conf. Proc. 879 (2007)
1793.
[4] T. Kaneyasu et al., J. Electron Spectrosc. Relat.
Phenom. 156-158 (2007) 279.
[5] Y. Hikosaka et al., submitted.
[6] R. R. Rye et al., J. Chem. Phys. 73 (1980) 4867.

116

Ⅲ -3. Atoms and Molecules

BL6U

Study on Deexcitation Processes Following the Cl 2p Photoexcitation ofCCl4 and HCl Molecules Using Two-Dimensional Electron Spectroscopy
H. Iwayama1, M. N. Piancastelli2,3,4, D. W. Lindle5 and E. Shigemasa1
1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
2
CNRS, UMR 7614, LCPMR, F-75005, Paris, France
3
Sorbonne Universités, UPMC Univ Paris 06, UMR 7614, LCPMR, F-75005, Paris, France
4
Department of Physics and Astronomy, Uppsala University, PO Box 516, SE- 75120 Uppsala, Sweden
5
Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003, USA
A molecular inner-shell excitation to the lowest
unoccupied anti-bonding orbital is generally followedby two competing processes: molecular dissociation
and resonant Auger decay. In particular, for hydrogen
halide molecules such as HBr [1] and HCl [2], it has
been shown that the molecular dissociation can befaster than the Auger decay. This process is referred
to as ultrafast dissociation [1,2]. In their resonant
Auger spectra, sharp peaks at electron energies
corresponding to the atomic Auger decays have been
observed. Two-dimensional electron spectroscopy(2D-ES), in which electron energy spectra arerecorded as a function of the photon energy, is one of
the most powerful methods to explore the decay
dynamics of inner-shell excited molecules. Here we
report on the result for the 2D-ES following the Cl 2p! 7a1* excitation for CCl4 molecules. As acomparison, we have also measured a 2D map
following the Cl 2p ! !* excitation for HClmolecules.
The experiment was performed on the soft X-ray
beamline BL6U at UVSOR. The photon energy
resolution E/!E was set to 2000. Kinetic energies ofthe emitted electrons were measured by ahemispherical electron energy analyzer (MBS-A1).
The direction of the electric vector was set to beparallel to the axis of the electrostatic lens of theanalyzer. The kinetic energy resolution of theanalyzer was set to 120 meV. The 2D maps wereobtained by taking spectra at a regular photon energy
interval of 100 meV across the resonances.
Figure 1 shows the 2D maps for CCl4 and HClmolecules measured in the Cl 2p excitation region. We
can find two sets of five prominent constant kinetic
energy lines in the photon energy range from 200 to
204 eV in Fig. 1(b). The two sets correspond to theatomic Auger decays of the Cl 2p3/2-1 and 2p1/2-1 states[2]. For the Cl 2p ! !* excitation of HCl molecules, alarge part of Auger decays occurs in the atomic
chlorine after the complete dissociation.
Then we look at the 2D map following the Cl 2p! 7a1* excitation for CCl4 molecules. As in the caseof HCl molecules, we can find two sets of prominent
constant kinetic energy lines in Fig. 1(a). Their
kinetic energies are the same as those of atomic
Auger lines in Fig. 1(b). This means that the ultrafast
dissociation process following the Cl 2p ! 7a1*

excitation for CCl4 molecules exists, where the C-Cl
bond is broken before the Auger decay. This behavior
can be explained by the fact that the 7a1* orbital ofCCl4 has a strong anti-bonding character which plays
a similar role as in the case the "* orbital in HCl.
However, we can clearly see other constant kinetic
energy lines in Fig. 1(a), which are not observed inFig. 1(b). They are attributable to the Auger decays
from molecular fragments. This fact strongly suggeststhat the atomic Auger decay is not predominant decay
processes for CCl4 molecules. The branching ratio of
molecular versus atomic Auger decays depends onthe mass of fragments. It is reasonable to consider
that the dissociation time for the CCl3 +Cl*(2p-13p6nl) fragmentation following the Cl 2p! 7a1* excitation in CCl4 is much longer than that for
the H + Cl*(2p-13p6nl) following the Cl 2p ! !*excitation in HCl. This reasonably explains thepresent observation.

Fig. 1. 2D-PES for (a) CCl4 and (b) HCl molecules
measured in the Cl 2p excitation region.
[1] P. Morin and I. Nenner Phys. Rev. Lett. 56 (1986)
1913.
[2] H. Aksela et al., Phys. Rev. A 41 (1990) 600.

117

Ⅲ-3

Ⅲ -3. Atoms and Molecules

BL6U

Decay Processes Following S 2p Photoexcitation of OCS Studied by
High-Resolution Two-Dimensional Electron Spectroscopy
1

H. Iwayama1, M. Simon2 and E. Shigemasa1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, JapanLCPMR, Université Pierre et Marie Curie, 75231 Paris Cedex 05, France2

Ⅲ-3

Molecular inner-shell photoabsorption spectra often
exhibit rich structures below the ionization thresholds,
which correspond to the excitations of an inner-shellelectron into unoccupied valence or Rydberg orbitals.
In the case of the molecules composed of lightelements, the inner-shell excited states are mainly
relaxed via Auger electron emission, andsubsequently fragmentation follows in general.
Thanks to the continuous works on high-resolution
resonant Auger electron spectroscopy, it has been
revealed that the nuclear motion of the molecularcore-excited states is promoted in competition with
the Auger decay.
In the previous report [1], angle-resolved two
dimensional (2D) electron spectroscopy, where theresonant Auger-electron spectra are measured as afunction of the photon energy, has been applied to thedeexcitation processes in the S 2p excitation region of
OCS with moderate energy resolution, and comparedto the previous work [2]. Here we present the 2D
maps following the S 2p3/2 → π* excitation withpreviously unprecedented resolution.
The 2D measurements were performed at BL6U.
The undulator radiation was monochromatized by avariable included angle varied line-spacing planegrazing monochromator. Concerning the 2D electron
spectroscopy, the monochromator bandwidth was set
to ΔEPh ~20 meV at hν=165 eV. Kinetic energy of theemitted electrons was measured by a hemisphericalelectron energy analyzer (MBS-A1) placed at a rightangle with respect to the incident photon beam
direction. The direction of the electric vector was set
to be either parallel (horizontal) or perpendicular(vertical) to the axis of the electrostatic lens of theanalyzer. The energy resolution of the analyzer was
set to ΔEk ~15 meV.
Figure 1 shows the 2D maps of resonant Auger
electron spectra following the S 2p3/2 → π* resonant
excitation of OCS measured in horizontal (a) andvertical (b) directions. The diagonal lines in Fig. 1 are
attributed to the valence photoelectron lines, whichclearly show vibrational side bands indicating that the
net energy resolution is far below 50 meV. The peakintensities for the valence photoelectrons in Fig. 1(a)are much stronger than those in Fig. 1(b), indicatingthat the β values for the valence shells are close to 2
in the vicinity of the S 2p ionization thresholds.
Clear island-like structures elongated in the verticaldirection are detected both in Fig. 1(a) and Fig. 1(b)in the kinetic energy region from 144 to 148 eV.

118

Three island-like structures with almost no dispersion
between 146.5 and 148 eV have been assigned tothree shake-up satellite states [2]. These states aredetected mainly in the lower photon energy regionand show almost isotropic angular distributions. For
the island-like structures with no dispersion in the
kinetic energy range from 144 to 146 eV, large
differences between Fig. 1(a) and Fig. 1(b) are seen.
To our knowledge, no assignments are given to thesestructures. In order to understand the origins of thestructures, sophisticated theoretical calculations arehighly desired.

Fig. 1. 2D maps of resonant Auger electron spectra
after the S 2p3/2 → π* excitation of OCS, measured athorizontal (a) and vertical (b) directions.
[1] L. Ishikawa, H. Iwayama and E. Shigemasa,
UVSOR Activity Report 40 (2013) 61.
[2] S. Masuda, T. Hatsui and N. Kosugi, J. Electron
Spectrosc. Rlat. Phenom. 137-140 (2004) 351.

Ⅲ -3. Atoms and Molecules

BL6U

Fluorine K Resonant Auger Decays of cis-Hexafluorocyclobutane
T. Kaneda1, S. Ishikawa1, K. Okada1, H. Iwayama2,3 and E. Shigemasa2,31

Department of Chemistry, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
states. We also found the peak shifts that change
almost linearly with the photon energy. The spectator
electron contributes to the screening in the
2-hole-1-electron final states, resulting in the peakshifts towards the higher kinetic energies.
The Auger-electron–photoion coincidence data
exhibit that the molecular ion in the F2s-1nF-1!*1
Auger-final states dissociates exclusively into thefragment ions without C–F bonds, namely, C+/CH+,
C2H2+ and F+. Further analysis is needed to state
conclusive results and is eagerly in progress now.

Inner-shell excited states of molecules relax into
various molecular cationic states through Auger
decays. The resultant cations are in general unstableand dissociate into fragment ions. Information on thecorrelation between the Auger-final states and the
products provides us deeper insight into thefragmentation dynamics of the inner-shell excitedmolecules. We found in our previous study that theC1s-1!CC* excited cis-1,1,2,2,3,4-hexafluorocyclobutane (cis-c-C4H2F6) molecule decays mainly into
the !CC-1v-1!CC* states, where v means a !CC or nF
outer-valence orbital, from which fragment ions suchas CHF2+ and CF+ are specifically formed [1]. This
report is based on our successive experiments
measured in the F 1s excitation region.
The experiments have been performed on the soft
X-ray beamline BL6U. The experimental setup has
been described in a previous paper [2]. The mainchamber was equipped with a pair of a double
toroidal electron analyzer (DTA) and an ion
time-of-flight mass spectrometer. Synchrotron
radiation was irradiated at right angles to the effusive
beam of the gaseous cis-c-C4H2F6 sample. The
electrons traveling through the DTA tube weredetected with a position sensitive detector (RoentDek,
DLD40). The pass energy was set to 400 eV in thisstudy. The electron spectra were acquired at thephoton energies including typical resonant peaks aswell as at the above-threshold energy of 707.5 eV.
The photoelectron spectrum was measured at 684.0
eV for subtracting the contribution from valence
ionization. The light intensity at each run wasmonitored downstream on the beamline. In addition,
Auger-electron–photoion coincidence data wereobtained at some photon energies.
Figure 1 shows a series of resonant Auger spectra
plotted on the final-state energy scale, after
subtracting the photoelectron components. The
normal Auger spectrum measured under the same
experimental conditions is also displayed at the top of
Fig. 1 on the double ionization energy (DIP) scale.
The DIP value for cis-c-C4H2F6 is evaluated to be
694.4 eV. The spectra present a great contrast to thosein the C 1s region [1]. The resonant Auger spectra
resemble the normal Auger spectrum well, indicatingthat the spectator Auger transitions predominate in
the F 1s region. We can assign the intense peak ataround 50 eV to the transition to the nF-1nF-1 final
states and at around 70 eV to that to the F2s-1nF-1

Ⅲ-3

Fig. 1. Resonant Auger spectra of cis-c-C4H2F6
acquired at a series of photon energies in the F 1s
region. The normal Auger spectrum measured at707.5 eV is also plotted at the top.
[1] S. Ishikawa, K. Okada, H. Iwayama, L. Ishikawa
and E. Shigemasa, UVSOR Activity Report 2012 40(2013) 58.
[2] T. Kaneyasu, Y. Hikosaka and E. Shigemasa, J.
Electron Spectrosc. Relat. Phenom. 156-158 (2007)
279.

119

Ⅲ -3. Atoms and Molecules

BL6U

Stability of Auger Final Dicationic States Following Core-Ionization of N2
Molecules Studied by an Auger-Electron−Ion Coincidence Method
H. Iwayama and E. Shigemasa

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, JapanⅢ-3

means that these fragmentation processes correlate to
the same dissociation limit. According to the NIST
Atomic Database, the corresponding dissociation
limit is N+(3P) + N+(3P).
It is seen in Fig. 2(a) that the Auger final states
ranging from 50 to 54 eV lead to N+(3P) + N+(3P).
According to the theoretical work [1], these Auger
final states are mainly attributed to the 1!u-2
configuration. Since the 1!u orbital has strong
bonding character, it is reasonable that the 1!u-2
dicationic states lead to the dissociation. It also turns
out that the Auger final states ranging from 46 to 50
eV and from 54 to 56 eV result in the production of
N2++. These Auger final states are mainly attributable
to the 3"g-2 and 3"g-11!u-1 configurations.

Absorption of a soft x-ray photon creates a corehole in a molecule. The core hole state is quite
unstable and usually decays via Auger-electron
emission for light elements. The Auger decay processleads to various dicationic states with two valenceholes. Although Auger final dicationic states are
generally unstable, and often come apart into ionicfragments due to the Coulomb repulsion between the
nuclear charges, metastable dications with lifetimes in
microsecond range are known to exist, depending on
the nature of their electronic states as shown in Fig. 1.
Here we report on the stability of Auger final states
following the 1s photoionization of N2 molecules byusing an Auger-electron−ion coincidence method.
The Auger-electron−ion coincidence measurements
were carried out on the undulator beamline BL6U at
UVSOR. The radiation from an undulator was
monochromatized by a variable included angle variedline-spacing plane grazing monochromator. The
electrons ejected at 54.7˚ with respect to the electric
vector of the incident radiation were analyzed inenergy by a double toroidal analyzer (DTA), whileions were extracted from the interaction region into a
momentum spectrometer by a pulsed electric fieldaccording to the electron detection. Arrival positions
on the detector and time-of-flights of ions wererecorded for every event. The pass energy of the DTA
was set to 200 eV for observing the Auger electrons.
The energy resolution was about 1.9 eV. All signals
from the detectors were recorded with an 8ch TDC
board. The photon energy was set to 450eV.
Figure 2 (a) shows a coincidence map for N2++ and+N production, in the binding energy region of the
dicationic states with two holes in the outer valenceorbitals. The vertical and horizontal axes correspondto the kinetic energy of ions and the binding energyof Auger electrons, respectively. Figures 2(b) and2(c) show the total ion kinetic energy distribution andAuger electron spectrum, which are gained byprojecting the counts on the map into the vertical andhorizontal axes, respectively. Although thetime-of-flights of the N2++ and N+ ions are the same
due to the same mass-to-charge ratio, they can easily
be distinguished from their kinetic energy differences,
as seen in Figs. 2(a) and (b). The peak at 0 eV in Fig.
2(b) is relevant to the metastable N2++ ions, while that
centered at 6 eV is associated with the N+ ions.
For (N+, N+) fragmentation processes, a strong
correlation between Auger-electron binding energies
and ion kinetic energies is detected in Fig. 2(a). The
slope of -1, which is represented by the broken line,

Fig. 1. A schematic representation of core ionizationand subsequent decay processes in N2.

Fig. 2. (a) Auger-electron−ion coincidence map forN2++ and N+ production. (b) and (c) represent the total
ion kinetic distribution and Auger electron spectrum
plotted on a binding energy scale, respectively.
[1] H. Agren, J. Chem. Phys. 75 (1982) 1267.

120

Ⅲ -3. Atoms and Molecules

BL6U

Decay Dynamics of Core-Excited HCl and H2S

1

M. N. Piancastelli1,2,3, D. W. Lindle4, R. Guillemin1,2, M. Simon1,2,
H. Iwayama5 and E. Shigemasa5

CNRS, UMR 7614, Laboratoire de Chimie Physique-Matière et Rayonnement, F-75005, Paris, France
Sorbonne Universités, UPMC Univ Paris 06, UMR 7614, Laboratoire de Chimie Physique-Matière etRayonnement, F-75005, Paris, France
3
Department of Physics and Astronomy, Uppsala University, PO Box 516, SE- 75120 Uppsala, Sweden
4
Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003, USA
5
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan2

We have obtained high-resolution resonant Auger
spectra in two isolated systems, HCl and H2S,
following Cl 2p and S 2p core excitation respectively.
The experimental results have been obtained as 2D
maps, namely by taking decay spectra at many photon
energy values spaced by 100 meV across the
below-threshold resonance regions up to above
threshold. The 2D maps allow one to follow in detailthe evolution of the spectral features, in terms of
relative intensity and dispersion law. We have alreadysuccessfully applied the same method to anothermolecular system, namely CF4 [1].
In Figs. 1 and 2 we show the 2D maps for HCl and
H2S. A wealth of spectral structures is present below
threshold in both cases. The different dispersion law(linear versus nonlinear behavior) is indicative ofspectral features related to molecular parent ions or to
fragments, Cl+ in HCl and HS+ in H2S. Theinterpretation of the spectral features is under way.
Together with the spectral assignment, another goalof the present experiments is to compare the dataobtained at UVSOR with another data set at the
moment under acquisition at the beam line
GALAXIES [2], SOLEIL, France.
There we will obtain 2D maps for the same systems,
but after 1s core excitation followed by radiative K!
decay. The intermediate state will be the same
(2p-1LUMO or 2p-1Rydberg), but prepared via two
different pathways, so we will be able to detect subtle
differences in the final states due to the different
decay dynamics in the two cases. In particular, wehave already demonstrated for HCl that during the
lifetime of the Cl 1s"LUMO core-excited state somenuclear motion takes place, resulting in a stretch of
the H-Cl chemical bond of about 0.1 A [3]. Therefore
the internuclear distance in the Cl 2p-1LUMO
core-excited state should be different if such state isreached by direct photoexcitation or by Cl
1s"LUMO excitation followed by K! decay. We
expect to locate the signature of such difference in the
decay spectra.

121

Ⅲ-3

Fig. 1. 2D map for HCl around the Cl 2p threshold.

Fig. 2. 2D map for H2S around the S 2p threshold.
[1] M. N. Piancastelli, R. Guillemin, M. Simon, H.
Iwayama, and E. Shigemasa, J. Chem. Phys. 138(2013) 23430.
[2] D. Céolin et al., J. Electron Spectrosc. Relat.
Phenom. 90 (2013) 188.
[3] M. Simon et al., Phys. Rev. A 73 (2006) 020706.

Ⅲ -3. Atoms and Molecules

BL6U

3d Hole Decay of the Isoelectronic Br and Kr+ 3d-14s24p6 Configurations
P. Lablanquie1, H. Iwayama2, K. Soejima3 and E. Shigemasa2

1

LCPMR, Université Pierre et Marie Curie, 75231 Paris Cedex 05, France
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Enviromental Science, Niigata University, Niigata 950-2181, Japan2

Ⅲ-3

We compare here the Auger decay of a 3d hole inthe same isoelectronic configuration 3d-14s24p6 but intwo different atoms. The aim is to test the influenceof the nucleus charge Z. Namely we compare thedecay of the Kr+ 3d-14s24p6 state (Z=36), created byphotoionization of the Kr atom, with that of the Br
3d-14s24p6 state (Z=35), created by ultra-fast dissociation of the HBr molecule upon 3d→σ* excitation [1].
The experiments were carried out on the soft X-ray
beamline BL6U at UVSOR. The monochro- matizedradiation was introduced into a gas cell filled withsample gas. Kinetic energies of the emitted electrons
were measured by a hemispherical electron energy
analyzer (MBS-A1) placed at a right angle relative tothe photon beam direction. The axis of theelectrostatic lens of the analyzer was set to be at themagic angle compared to the polarization direction of
the incident light. The energy resolution of theanalyzer was set to ~12 meV. The monochromator
exit slit opening was set to 300 µm, whichcorresponds to a resolving power of ~1000.
Figure 1 displays a Kr+ 3d Auger spectrum. It was
obtained at 99 eV photon energy in order to avoid
contamination by the decay of 3d satellite states. The
main Auger lines are grouped in 3 zones, associatedwith the formation of the Kr2+ final states of 4s14p5,
4s24p34d and 4s04p6 configurations [2]. The Double
Auger decay produces electrons of 0 to ~22 eV [3].
The ultra-fast dissociation of the HBr 3d→ σ*resonance is known to produce an excited atomic Br*
3d-14s24p6 fragment [1] after the dissociation. In 2012
we showed that the equipment at UVSOR allows one
to measure the Auger electron spectrum of the Br*
fragment with an unprecedented resolution. Here, we
extend this work to the complete Auger spectrum.
Figure 2 (top red) displays the result directlycomparable to the Kr+ case of Fig. 1, which was
obtained by combining the measurements on the 3d3/2
and 3d5/2 → σ* resonances. One observes a similar
distribution for the Kr2+ and Br+ final states of 4s14p5
and 4s04p6 configurations, but the structures of the‘satellite’ states of a 4s24p34d configuration are richer
in Br+ than Kr++, suggesting the sensitivity of the 4dorbital to the Z value of the core. Another marked
difference is the energy region where double Auger
decay contributes. From energetics reasons [4], it isexpected to be wider in the Br case, producing
electrons up to ~32 eV. The 4s04p6 Br+ states are thus
predicted to decay further. Finally a measurement on
the 3d5/2 → σ* resonance (Fig. 2, bottom) isolates thelines associated with the decays of the 3d5/2 hole,
without the need of coincidence experiments used in
the Kr+ case [3].

Fig. 1. Auger spectrum following the decays of a 3dhole in Kr+ 3d-14s24p6.

Fig. 2. Auger spectrum following the decays of a 3dhole in Br 3d-14s24p6. Top (red) is directlycomparable to the Kr case. Bottom (blue) was
measured on the HBr 3d5/2 → σ* resonance andselects essentially the 3d5/2 hole decays.
[1] P. Morin and I. Nenner, PRL 56 (1986)1913.
[2] J. Jauhiainen et al., J. Phys. B 28 (1995) 3831.
[3] J. Palaudoux et al., PRA 82 (2010) 043419.
[4] http://physics.nist.gov/asd122

Ⅲ -3. Atoms and Molecules

BL8B

Ultraviolet Photoelectron Spectra of Tm2@C82 (III) and Tm2C2@C82 (III)T. Miyazaki1, Y. Tokumoto1, R. Sumii2,3, H. Yagi1, N. Izumi4, H. Shinohara4 and S. Hino1
Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan
2
Institutes for Molecular Science, Okazaki, 444-858, Japan
3
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan
4
Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

Fullerenes cages often encapsulated metal atom(s)and metal-carbide clusters, and entrapped metalatom(s) donate electrons to the cage, which induce
the change in their electronic structure. As formono-metal atom and multiple atoms encapsulated
C82, the oxidation state of encapsulated metal atom iseither +2 or +3. We have been measuring theultraviolet photoelectron spectra (UPS) of endohedral
metallofullerenes and revealed their valence band
electronic structure [1-3]. In the course of theinvestigation a following empirical rule has been
established: the UPS in the upper binding energy
region (Eb < 5 eV) were significantly different wheneither the cage structure or the amounts of transferred
electrons is different. Recently, Tm atoms and Tm2C2
encapsulated C82 fullerenes, Tm2@C82 (III) andTm2C2@C82 (III), have been isolated. In this report,
the UPS of Tm2@C82 (III) and Tm2C2@C82 (III) arepresented and are compared with those of otherendohedral fullerenes.
The UPS were measured at BL8B of UVSOR
facility of Institute for Molecular Science. The basepressure of the UPS measurement chamber was
4!10-8 Pa and the pressure during the measurement
was about 6!10-8 Pa. The measured UPS werereferenced against the Fermi level (EF) of gold andwere plotted as a function of binding energy relative
to EF. All UPS were normalized by the peak height ofa structure appeared at around 5.5 eV.
The UPS of Tm2@C82 (III) and Tm2C2@C82 (III)obtained with hv = 20 ~ 60 eV incident photon energy.
The UPS of two metal atoms encapsulated endohedral
fullerenes Y2@C82-C3v, Er2@C82-C3v and Tm2@C82(III) (M2 group), and those of metal-carbide (M2C2)
encapsulated
metallofullerenes
Y2C2@C82-C3v,
Er2C2@C82-C3v and Tm2C2@C82 (III) (M2C2 group)
obtained by 40eV photon energy are shown in Fig. 1
for comparison. The UPS of the M2 group are almost
identical; the peaks of structures A – C appear at thesame binding energy region with almost the same
intensity. Resemblance of these UPS suggests that theelectronic structure of the M2 group is almost identical.
Since the electronic configuration of Er2@C82 andY2@C82 was determined to be M26+@C826-, theoxidation state of Tm atom in Tm2@C82 can be
deduced to be +3. This finding is rather surprisingsince the oxidation state of Tm atom in Tm@C82 is+2. The UPS of the M2C2 group are also identical,
which suggests their analogous electronic structure.

123

The UPS of groups M2 and M2C2 show goodcorrespondence among them; three structures A – C
appear at more or less the same energy region. The
comparison of the UPS of Y2@C82 (II) and Y2C2@C82(II) suggested that the electronic configuration of
Y2C2@C82 is (YC)24+@C824+.
Present findings of the oxidation state of entrapped
Tm atom(s) are rather surprising. The oxidation stateof Tm atom is easily changed when the number ofentrapped atoms is changed. When Y atom(s) areentrapped in the C82 cage, the oxidation state of Y
atom is +3, and it is independent on the number ofentrapped atoms. The most stable oxidized form of acompromise to have the stable electronic states of the
C82 cage and Tm atoms.
UPS
h# = 40 eV

& '
(
$

%

"-bond
Photoelectron
counts

1

C B A
C' B'
A'
Tm2C2@C82
Er2C2@C82
Y2C2@C82& 'Tm2@C82($%

Er2@C82!-bond
C B A
C' B'
A'

Y2@C82

onset

12

10

8

6

4

2

Binding Energy / eV

0 = EF

Fig. 1. UPS of M2@C82-C3v and M2C2@C82-C3v(M=Y, Er, Tm) with hv = 40 eV.
[1] S. Hino et al., Bull. Chem. Soc. Jpn. 82(2009) 963.
[2] T. Miyazaki et al., Chem. Phys. 378 (2010) 11.
[3] T. Miyazaki et al., Chem. Phys. 397 (2012) 87.

Ⅲ-3