რ
ChemistryⅢ-3 Chemistry

BL4B

Ligand Field in Fe-based spin-crossover Coordination Polymer Revealed bySoft x-ray Absorption Spectroscopy
K. Yamagami
Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1, Sayo-cho, Sayo-gun, Hyogo 679–5198, JapanThe 3d transition metal elements have many attractive
physical phenomena in solid-state materials such as
unconventional superconductivity, metal-insulatortransition, and spin transition involving magnetism dueto their high charge, spin, and orbital degrees of
freedom. Since the 3d electronic states in solids arecontrolled by “ligand field eﬀects” due to the type andsymmetry of ligands and “charge transfer interactions”
between transition metal ions via ligands, experimental
exploration of element-specific electronic states
provides fundamental information for understanding
macroscopic properties involving 3d electrons.
In this study, I focus on “spin crossover,” which isstrongly related to ligand field eﬀects and spin degrees
of freedom. Spin crossover is a phenomenon in which achange in the splitting width of the 3d orbital levelcauses an electron spin transition. In particular, the spincrossover transition that appears in transition metal
coordination polymers exhibits thermal hysteresis.
Since the transition temperature and the shape of thehysteresis depend on the guest molecules encapsulated
in the coordination polymer, it is attracting attention asa new adsorption material along with activated carbon
and silica gel. However, spectroscopic element-specificanalysis of the 3d orbital levels associated with thermal
spin-crossover transitions in coordination polymers ischallenging due to their low chemical stability against
light source irradiation.
In this work, I performed the soft x-ray absorption
spectroscopy (XAS) for the Fe-based spin-crossovercoordination polymer Fe(pyrazine)2[Pt(CN)4] toinvestigate the contribution of ligand field eﬀect for
Fe2+ ions under the tetragonal symmetry related to thethermal spin crossover transition.
The XAS measurement was done at UVSOR BL4B.
The Fe L2,3-edge XAS spectra was recorded by the total
electron yield (TEY) and partial fluorescence yield(PFY) modes obtained by the drain current for TEY and
SDD detector for PFY, respectively. The powder
samples were thinly expanded on the carbon tape andits temperature was controlled by the liq.N2 and ceramicheaters. During measurement, the x-ray irradiateddamage of the samples was checked from the position
and irradiation time dependence of the XAS spectra.
The energy calibration was done by the Fe L2,3-edge
XAS spectra of Fe3O4. All XAS spectra were normalized
by the incoming x-ray flux.
In this report, I show the XAS results in PFY mode
since the huge noise was observed in TEY mode. Fig.1
shows the temperature dependent Fe L2,3-edge XAS
spectra. During one cycle of temperature change, I

observed a spectral change corresponding to thetransition between the high-spin (HS) state at hightemperature and the low-spin (LS) state at lowtemperature and found that the transition temperature
diﬀers between the heating and the cooling processes.
According to the simplest Fe2+ ionic model calculations,
the Fe2+ ions have only HS state at 320 K and only LS
state at 240 K. Therefore, I carried out the linear fitting
analysis by the spectra at 320 K and 240 K to estimate
the spin state weight around spin-crossover transition.
The fitting results reproduce the experimental spectra
and plotted as the function of the temperature together
with the macroscopic magnetometry result ofFe(pyrazine)2[Pt(CN)4] (Fig.2). I found that thetransition temperature between XAS spectra andmagnetization is quite diﬀerent, seemingly linking to
the diﬀerent thermal stability between the electronic
state and structural distortion.

Fig. 1. The temperature dependent Fe L2,3-edge XAS
spectraandfittinganalysis
resultofFe(pyrazine)2[Pt(CN)4].

Fig. 2. The spin state wight of Fe2+ ions as the functionof the temperature.

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BL1U

Monitoring Phase Diﬀerence between Magnetic Substates in Helium Atom
T. Kaneyasu1,2, Y. Hikosaka3, M. Fujimoto2,4, H. Iwayama2,5 and M. Katoh2,6
1
SAGA Light Source, Tosu 841-0005, Japan
Institute for Molecular Science, Okazaki 444-8585, Japan
3
Institute of Liberal Arts and Sciences, University of Toyama, Toyama 930-0194, Japan
4
Synchrotron Radiation Research Center, Nagoya University, Nagoya, 464-8603, Japan
5
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
6
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
2

Quantum manipulation of populations and reaction
pathways in matter using the coherence properties oflight, so-called coherent control, is currently one of thehottest research areas in optical physics andphotochemistry. We have recently shown thatsynchrotron light is a new tool for achieving coherent
control in the XUV and attosecond regimes [1–3]. Thismethod is based on the use of the longitudinal coherenceof individual light wave packets comprising incoherent
radiation pulses. In all of these experiments, a pair oflight wave packets was used to produce a pair ofelectron wave packets that interfere in a single atom.
The quantum phase diﬀerence between the electron
wave packets determines the behavior of the controlled(or probed) quantum state, and can be precisely
controlled by varying the time delay between the lightwave packets at the attosecond level. In this report, we
present another approach to orbital alignment controlof helium atoms [2] to monitor the phase diﬀerence
between the interfering wave packets. The quantum
phase diﬀerence between coherently excited magnetic
substates is visualized as a quantum beat that appears in
the fluorescence decay curve [4].
The experiment was performed at undulator beamline
BL1U of the UVSOR-III synchrotron. A tandem
undulator consisting of twin APPLE-II type variable
polarization devices was operated in helical mode,
providing pairs of 10-cycle left- and right-circularly
polarized light wave packets. The central frequency of
the fundamental radiation was set to about 24 eV. To
measure the fluorescence decay curve of helium atoms,
the UVSOR-III synchrotron was operated in the single
bunch mode. The fluorescence photons emitted fromhelium atoms were detected by a photomultiplier tube.
A magnetic field of approximately 20 G was applied
parallel to the light propagation axis in the interaction
region to induce Zeeman splitting between the magnetic
substates of helium atoms.
Figure 1 shows fluorescence decay curves of 1s6p
excited state of helium atoms measured at eightdiﬀerent settings of the time delay τ between the lightwave packets. The quantum beat oscillations
superimposed on the exponential decay with a lifetimeof 13.1 ns are visible and the initial phases of theoscillations shift by varying the time delay. The

theoretical curves well reproduce the quantum beatstructures observed in the measurement. Quantum beatmeasurement thus enables visualization of the quantum
phase that has been used as a control knob for quantum
manipulation of atomic systems

Fig. 1. Zeeman quantum beat in fluorescence decay ofhelium atoms [4]. The quantum phase ωτ is set toincrease from 0 to 7π/2 with a step size of approximately
π/2 where ω is the resonance frequency from the groundstate to the 1s6p state. The experimental data points areshown by gray circles and the red curves represent thecalculation results[1] Y. Hikosaka et al., Nat. Commun. 10 (2019) 4988;
ibid. 12 (2021) 3782.
[2] T. Kaneyasu et al., Phys. Rev. Lett. 123 (2019)
233401.
[3] T. Kaneyasu et al., Phys. Rev. Lett. 126 (2021)
113202.
[4] T. Kaneyasu et al., J. Phys.: Conf. Ser. 2380 (2022)
012115.

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Ⅲ-3 Chemistry

BL1U

High-Resolution Measurement of State-Resolved Photoelectron Circular
Dichroism with Varied Photoionization Energies
H. Kohguchi1, Y. Hikosaka2, T. Kaneyasu3, S. Wada1, H. Ota4, M. Katoh1,4 and Y-I. Suzuki5
1

Graduate School of Advanced Science and Engineering, Hiroshima University,
Higashi-Hiroshima 739-8526, Japan
2
Institute of Liberal Arts and Sciences, University of Toyama, Toyama 930-0194, Japan
3
SAGA Light Source, Tosu 841-0005, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Medical Technology, Health Sciences University of Hokkaido, Tobetsu, 061-0293, Japan

Measurements of photoelectron circular dichroism(PECD) require high-quality radiation for ionizing
chiral molecules. One-photon photoionization in thevacuum ultraviolet region provides a fundamental
understanding of the physical origin of PECD. Thus,
we launched the PECD measurements at BL1U on
February 2020. In the beginning of the feasibility test,
the undulator conditions for circularly polarized light
were optimized for a particular electron beam orbit,
which was not used in regular beam time operation. In
2022, the normal electron beam orbit applicable to
BL1U was developed so that the PECD measurements
were possible in regular beam time. With the alternationof the electron beam orbit, the arrangement of theBL1U line was reformed.
We have employed a monochrometer to reduce thespread of photon energy to measure the state-resolved
PECD of chiral systems. The monochrometer line withtwo mirror chambers is inserted between the BL1U
port and our velocity-map imaging (VMI) apparatus(Fig. 1). We also modify the imaging device in thisbeam time. Our original setup used a resistive anodebacked by an MCP detector to obtain the photoelectron
images. We have replaced an imaging system consistingof a phosphor screen and a CCD camera with the anodetype imager. The benefit of the optical camera system isreal-time imaging during the measurement, which is
expected to be advantageous in eﬃcient searching forexperimental conditions. Improved performance due tothe renewal of the electron beam condition and theimaging system is evaluated in comparison with theprevious PECD data [1].
We measured the PECD of methyl oxirane (CH3C2H3O) in the new experimental setup. The PECD
appears as asymmetric forward/backward intensitywith respect to the circularly polarized light propagation.
The result almost reproduced the previous data in thatthe forward-backward asymmetry (red/blue in Fig. 2)
exhibited distinct state-dependence. The quality of the
PECD data is the contrast of the forward/backward
asymmetry, which is presented by blue/red contrast in
the diﬀerence images of the right and left circularpolarization in Fig. 2. The imaging system with thecamera provides an analog (Fig. 2(a)) and a counting(Fig. 2(b)) integration modes. The better PECD data
was obtained by analog integration, although it isgenerally inferior to the counting mode in accuracy.
This can be due to the too-slow counting integration of
the software compared to the photoelectron counting
rate. The renewal of the setup potentially improve our
PECD measurements; however more detailed
examination of several signal properties is necessary.
yFig. 1. New arrangement of the VMI apparatus for
PECD measurements with a monochrometer at theBL1U beamline.

Fig. 2. Photoelectron circular dichroism (PECD)
images of s-methyl oxirane measured with (a) analog
integration mode and (b) counting integration mode.
The propagation direction of the photoionization
radiation is vertical in the figures.
[1] H. Kohguchi, Y. Hikosaka, T. Kaneyasu, S. Wada,
H. Ota, M. Fujimoto, M. Kato and Y-I. Suzuki, UVSOR
Activity Report 49 (2021) 106.

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BL2A

M4,5-edge XANES Spectra of La and Nd Complex Oxides
H. Asakura 1, M. Konno 1 and K. Nanakarage 1
1

Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, Kowakae,
Higashiosaka, Osaka 577-8502, JapanThe areas of the pre-edge region at the lanthanide(Ln) L1-edge XANES spectra and the full with half
maximum of the white line at the Ln L3-edge XANES
spectra have been found to be good indicators of thelocal structure or symmetry of Ln elements in complex
oxides [1-3]. However, it is usually diﬃcult to obtain
detailed electronic and/or geometric information of theLn elements because of the inherent low energy
resolution of Ln L-edge XANES spectra. Then, theM-edge XANES spectra, which are potentially much
more sensitive to electronic structure, are employed toobtain more detailed information on the local structure.
However, there are very few reports on the measurementof M-edge XANES spectra of Ln elements. In thisstudy, we measured the M-edge XANES spectra of La
or Nd complex oxides to investigate whether they canbe used as indicators of local structure.
We prepared various La and Nd complex oxides by apolymerized complex method and confirmed that single
phase polycrystalline powders were obtained by their
XRD patterns. Nd M4,5-edge XANES spectra wereobtained at BL2A, UVSOR using a Beryl doublecrystal monochromator. We put each powder sample
onto indium (In) foil bonded to the sample holder withcarbon tape for total electron yield method measurement.
To the best of our knowledge, there are no wellestablished data analysis procedure on the M-edge
XANES spectra even for basic background removal or
normalization. On the present data, we performed
background removal in the pre-edge region below theM5-edge and normalization in the post-edge region
above the M4-edge with Athena included in the Demeter
package [4].
The Nd M4,5-edge XANES spectrum of Nd2O3,
NdAlO3, NdMnO3, and Nd2CoO4 was very similar toeach other (Fig. 1), which indicated the oxidation stateof Nd was the same, trivalent. By a closer look into thespectra, we found diﬀerence in relative absorbance ataround 1006, 1008, and 1010 eV marked as peak A, B,
and C at the Nd M4-edge XANES region (Fig. 2). The
main contribution for the peak A and B is ascribed tothe transition obeying the selection rule ∆J = 0, andpeak C is to ∆J = −1, respectively [5]. In addition,
theoretical simulation of Pr M4,5-edge XANES of Pr3+,[PrF6]3-, [PrCl6]3-, and [PrBr6]3- indicates possible
sensitivity to the local structure of Pr [5]. However, atpresent, we do not have plausible interpretation of thesecharacteristic features.
On the other hand, there are some questions as towhether the validity of the spectra can be guaranteed.
For example, it is possible that diﬀerences due tocharge-up or slight variations in X-rays may be reflected
into the spectra. In fact, on NdAlO3, significant
diﬀerence was observed at another facility when theenergy sweep direction was from the low energy to thehigh energy and from high to low, and the eﬀect ofcharge-up was suspected. Thus, further careful study isneeded.

Fig. 1. Nd M4,5-edge XANES spectra of Nd complex
oxidesFig. 2. Nd M4-edge XANES spectra of Nd complex
oxides[1] H. Asakura et al., Inorg. Chem. 53 (2015) 6048.
[2] H. Asakura et al., J. Phys. Chem. C 118 (2014)
20881.
[3] H. Asakura et al., Inorg. Chem. 60 (2021) 9359.
[4] B. Ravel, M. Newville, J. Synchrotron Rad. 12(2005) 537.
[5] H. Ramanantoanina, J. Chem. Phys. 149 (2018)054104.

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Ⅲ-3 Chemistry

BL3U

O K-edge XAS of Photoreactions in Dissolved Oxygen on Lipid Bilayer
F. Kumaki1, 2, M. Nagasaka3, 4, Y. Kinjo5, R. Tero5, Y. Okano3, M. Fujimoto3, 4 and J. Adachi1, 2
1

Institute of Materials Structure Science, High Energy Accelerator Research Organization,
Tsukuba 305-0801, Japan
2
School of High Energy Accelerator Science, The Graduate University for Advanced Studies (SOKENDAI),
Tsukuba 305-0801, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
5
Toyohashi University of Technology, Toyohashi 441-8580, Japan

Porphyrin dyes form triplet states by thephotoexcitation and relaxation process due to lightabsorption. Singlet oxygen (1O2) is generated by theenergy transfer from the triplet state of the porphyrin to
the surrounding oxygen molecule with ground triplet
state (3O2). Singlet oxygen is highly reactive, and thegeneration of singlet oxygen by photosensitizers suchas porphyrins is used for a cancer treatment as aphotodynamic therapy [1]. The experimentally researchof the elementary processes of singlet oxygen
production in a wet environment like in vivo conditions
or in liquid is important for the development ofchemistry and medicine.
From O K-edge X-ray absorption spectroscopy(XAS), we planned to measure the electronic state ofsinglet oxygen generated in solution directly via laser
excitation of photosensitizers. We have recently
developed and demonstrated the time-resolved XAS
system for optical reactions in liquid samples by asynchronizing synchrotron radiation pulse and a laser
pulse at KEK Photon Factory [2]. At the UVSOR, wehave been developed a similar time-resolved XAS
system by synchronizing soft X-ray pulses (530 eV,
128 ps) and visible laser pulses (400 nm). Since thelifetime of singlet oxygen in liquid is ~3 μs [3], thesynchrotron radiation pulse whose pulse duration isabout 100 ps, is suitable to observe its dynamics. In thisreport, the change of XAS spectra between the groundstate and the state under laser irradiation was measured.
The O K-edge XAS spectra were measured by using
the liquid flow cell at BL3U. The liquid cell consists ofa liquid layer sandwiched between two Si3N4
membranes on which lipid bilayers were prepared. The
buﬀer solution (NaCl 100 mM, HEPES 25 mM)
bubbled with oxygen gas was continuously pumped
into the cell at a flow rate of 100 μl/hr to keep the
dissolved oxygen on the lipid bilayer. The emphasizedpeak of dissolved oxygen on the lipid bilayers can bemeasured by thinning the liquid layer to the limit [4].
For the formation of singlet oxygen with aphotoreaction, the chlorophyll-a was used as aphotosensitizer and was added to the lipid bilayer. By
irradiating the visible laser (400 nm, 0.5mW) which issecond order harmonic generation (SHG) of Ti:sapphirelaser to the cell, the chlorophyll-a was photoexcited.

We attempted to observe singlet oxygen produced from
dissolved oxygen by the energy transfer from the triplet
state of chlorophyll-a caused by the photoexcitationand the relaxation process. The O K-edge XAS spectraof dissolved oxygen in the ground state and during laser
irradiation were compared, and the diﬀerence wasobserved.
Figure 1 shows the O K-edge XAS spectra of lipid
bilayer. The peak around 531 eV is assigned as
dissolved oxygen molecules adsorbed on lipid bilayers.
The spectrum of the state during laser irradiation (laseron) shows the lower photon energy shift compared tothat in the ground state (laser oﬀ). We will discuss theformation mechanism of singlet oxygen from thediﬀerence spectrum with the help of the inner-shell
calculations.

Fig. 1. O K-edge XAS spectra of dissolved oxygen,
whose peak positions are around 531 eV, on lipid
bilayers. The green and blue lines are the ground state(laser oﬀ) and the state under laser irradiation (laseron), respectively.
[1] M. Ethirajan et al., Chem. Soc. Rev. 40 (2011) 340.
[2] F. Kumaki et al., J. Chem. Phys. 158 (2023) 104201.
[3] C. A. Long and D. R. Kearns, J. Am. Chem. Soc. 97(1975) 2018.
[4] F. Kumaki et al., UVSOR Activity Report, 49 (2022)
118.

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BL3U

Carbon K-edge X-ray Absorption Spectra of Liquid Ethanol Reproduced by
Quantum Chemical Calculations and Molecular Dynamics Simulations
M. Nagasaka1, 2
1Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan

2

Liquid ethanol (EtOH) shows complicated liquid
structures with the continuous formation and decay ofhydrogen bond networks including the hydrophobic
interactions between ethyl groups. Soft X-ray
absorption spectroscopy (XAS) has potential toinvestigate the structures of liquid EtOH separating thecontributions of the hydrogen bond interactions andhydrophobic interactions between ethyl groups.
Recently, we have measured C K-edge XAS of liquid
EtOH by using a transmitted-type liquid cell [1].
However, the inner-shell spectra of the model structures
did not reproduce the spectral shapes of liquid EtOH
since the liquid structures reconfigured continuously. In
this study, we have performed C K-edge inner-shell
calculations of liquid EtOH by the summation of thecalculated spectra of excited EtOH molecules withneighbor molecules extracted from the liquid structures
obtained by the molecular dynamics (MD) simulations[2].
MD simulations of liquid EtOH were conducted byusing the program package GROMACS [3]. The
equilibrium structure including one thousand EtOH
molecules were obtained after a simulation time of 101
ns at 25 °C and 1 atm in the isobaric-isothermal
ensemble. The inner-shell calculations were conductedby using the program package GSCF3 [4]. The groundand core excited states were calculated within the
Hartree-Fock method, namely, ΔSCF (self-consistent
field). As shown in the inset of Fig. 1, we have extracted
one thousand small liquid structures that consist of
excited EtOH molecules and neighbor EtOH molecules
within the CH2-CH2 distance of 6 Å from the excited
EtOH molecules. The inner-shell spectrum of liquid
EtOH was obtained by the summation of one thousand
calculated spectra of small liquid structures.
Figure 1(a) shows the experimentally obtained C
K-edge XAS spectrum of liquid EtOH [1]. The
spectrum shows four peaks: The peak at 287.311 eV is
the transition of the CH3 C 1s electron to the 3s-type
Rydberg orbital (CH3 3s). The peaks at 288.025 eV and
288.760 eV are assigned as the transition of the CH3 C
1s electron to the 3p-type Rydberg orbitals (CH3 3p1
and 3p2). The peak at 289.710 eV is assigned to thetransition of the CH2 C 1s electron to the 3s-type
Rydberg orbital (CH2 3s). Figure 1(b) shows thecalculated inner-shell spectrum of liquid EtOH fromthe summation of one thousand calculated spectra ofsmall liquid structures. The calculated spectra well
reproduced four Rydberg peaks and spectra shapes

obtained by the experiments. However, the calculated
higher energy shifts from gas to liquid phases areoverestimated compared to the experimental values. It
is because the induced polarization of the surrounding
EtOH molecules above the CH2-CH2 distance of 6 Å isignored, which causes the lower energy shifts of the
XAS peaks. We have also calculated C K-edge innershell spectra of liquid methanol and confirmed that thecalculated spectra well reproduced the experimental
results [5].

Fig. 1. C K-edge XAS spectra of liquid EtOH from (a)experiments and (b) calculations. The inset shows oneof the liquid structures used for the inner-shell
calculations, where EtOH molecules were extracted
from the liquid structure within the CH2-CH2 distanceof 6 Å from the central EtOH molecule.
[1] M. Nagasaka et al., J. Phys. Chem. B 126 (2022)
4948.
[2] M. Nagasaka, J. Chem. Phys. 158 (2023) 024501.
[3] M. J. Abraham et al., SoftwareX 1-2 (2015) 19.
[4] N. Kosugi, Theor. Chim. Acta 72 (1987) 149.
[5] M. Nagasaka et al., J. Phys. Chem. B 118 (2014)4388.

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Ⅲ-3 Chemistry

BL3U

Observation of the Behavior of Sumanene in Organic Solventsby C K-edge XAS Experiment
Y. Uetake1,2, K. Sugimura1, R. Ihsan1, M. Nagasaka3 and H. Sakurai1,2
1Division of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan
Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI),
Osaka University, Suita, 565-0871, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan2

0.8

C K-edge XAS

C = C ʋ *0.6
triphenylene

Intensity

Sumanene, a bowl-shaped π-extended molecule, hasbeen found to exhibit a unique columnar packing
structure in the crystalline state due to the intermolecularCH–π interactions between them[1]. Such interactions
are expected to occur in the solution state. Previously,
our group reported the infrared spectroscopy ofsumanene in para-H2 matrix. However, there are still
few reports on the dynamic behavior of π-conjugatedmolecule, including sumanene, in solution state. In thisstudy, we performed solution-phase X-ray absorption
spectroscopy (XAS) of π-extended molecules toinvestigate dynamic behavior, such as intermolecularinteractions, in organic solvents.
The solution-phase C K-edge XAS experiments were
performed at soft X-ray beamline BL3U using atransmission-type liquid flow cell[2]. Sumanene (1),corannulene (2), and triphenylene (3) were dissolved in
tetrahydrofuran, respectively, to give sample solutions(10 mmol/L). The thus-prepared solution was injectedto the cell by syringe. After adjusting the optical path
length by controlling helium pressure, XAS experiment
was conducted.
Fig. 1 shows C K-edge XAS data of sumanene,
corannulene, and triphenylene, respectively. In the caseof sumanene, relatively sharp peak was observed at285.2 eV, which is assigned as the transition of C 1s
electron to C=C π* orbitals. Meanwhile, two peaks
were observed at 284.8 and 285.3 eV. This result
indicated the diﬀerence of the electronic structure
between sumanene and corannulene. Inner-shell
calculations were performed using GSCF3 program[3,4]and it was found that the simulated peak pattern wasmatched with experimental spectra in the case ofsumanene and corannulene, although these calculations
did not reproduce the relative energy value (Fig. 2).
From this calculation, it was found that the peak at
284.8 eV corresponds to the internal carbons of
corannulene. Interestingly, XAS data for triphenylene
showed two split peaks, unlike the case of sumanene.
Since the inner-shell calculations of sumanene andcorannulene exhibited almost the same spectral shape,
the spectroscopic diﬀerence is thought to represent thediﬀerence in the behavior in solution.

0.4
corannulene

0.2

sumanene

10 mmol/L in THF

0.0
283.5

284.0

284.5

285.0

285.5

286.0

286.5

Energy (eV)Fig. 1. C K-edge XAS data of sumanene, corannulene,
and triphneylene.

Fig. 2.
Inner-shell calculations of sumanene,
corannulene, and triphneylene.
[1] H. Sakurai, T. Daiko, H. Sakane, T. Amaya and T.
Hirao, J. Am. Chem. Soc. 127 (2005) 11580.
[2] M. Nagasaka and N. Kosugi, Chem. Lett. 50 (2021)
956.
[3] N. Kosugi and H. Kuroda, Chem. Phys. Lett. 74(1980) 490.
[4] N. Kosugi, Theor. Chim. Acta 72 (1987) 149.

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BL3U

Operando Observation of Adsorbed Anions on the Surface of Nickel
Catalysts by Soft X-ray Absorption Spectroscopy
A. Sakai1, Z. Li1, K. Harada1, S. Tsunekawa1, M. Nagasaka2 and M. Yoshida1,3
1

Yamaguchi University, Tokiwadai, Ube, Yamaguchi 755-8611, Japan
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
3
Blue Energy Center for SGE Technology (BEST), Ube, Yamaguchi 755-8611, Japan
2

Recently, electrochemical hydrogen production fromwater has been attracting attention to develop asustainable society. In this system, nickel oxides
electrodeposited in carbon electrolyte solution are
known to be one of the eﬃcient electrocatalyst foroxygen production [1-2]. Thus, various operando
spectroscopic analyses have applied to the nickel
catalysts in order to reveal the physical properties andfunctions. However, the role of carbonate anion in theelectrolyte solution is still not fully understood. From
this background, in this study, the role of adsorbed
carbonate anion was investigated for the nickel
electrocatalysts by X-ray absorption fine structure(XAFS) measurements using hard X-ray and soft X-ray
under operando conditions.
The handmade electrochemical cell was used with a
Pt wire counter electrode and an Ag/AgCl referenceelectrode (NaCl). The nickel electrocatalysts wereprepared by electrodeposition on Au thin film in asolution containing Ni2+ and carbonate anion (Ni-Ci
catalyst). The operando Ni K-edge XAFS were carriedout by fluorescence mode in the SPring-8 BL01B1, andthe operando C K-edge XAFS were performed bytransmission mode at BL3U in the UVSOR synchrotron.
First, SEM, EDX, UV-vis and XPS measurements
were also measured to investigate the surface
morphology and chemical states of electrodepositedcatalysts. Next, we tested the electrochemical activityof oxygen evolution reaction (OER), suggesting thatthe prepared Ni-Ci functioned as highly eﬃcient OER
electrocatalyst. Moreover, the electrolyte solution was
exchanged from potassium carbonate solution (K-Ci) topotassium phosphoric solution (K-Pi) during monitoring
the OER activity, indicating that the water splitting
activity of the Ni-Ci catalyst was preserved in the K-Pi
electrolyte solution.
The operando Ni K-edge XAFS measurements were
performed to investigate the electronic state and local
structure of the Ni-Ci catalyst. The result of EXAFS
analysis showed that the peaks of Ni-O and Ni-Nibonds were observed at similar positions compared tothe γ-NiOOH reference sample, suggesting that the
local structure of Ni in the catalyst was consistent withthat of γ-NiOOH. Moreover, the local structure of thecatalyst in the K-Pi solution was also maintained that of
γ-NiOOH.

Finally, the operando C K-edge XAFS measurements
were carried out for the Ni-Ci catalyst under thecatalytic reaction (Fig. 1). The result showed thatcarbonate anions were adsorbed on the catalyst surface.
The adsorbed peak was remained even after exchanging
the electrolyte solution from K-Ci to K-Pi. Thus, thisresult suggests that the carbonate anions are strongly
adsorbed on the Ni-Ci catalyst. The adsorbed carbonate
anions are likely to contribute the stabilize the γ-NiOOH
structure with high oxidation number Ni. On the basisof these discussions, we concluded that the γ-NiOOH
structure stabilized by adsorbed carbonate anions could
eﬃciently decompose water molecule to oxygen gas
due to the high oxidation number Ni of active site.

Fig. 1. Operando C-K edge XAFS spectra for Ni-Ci
electrocatalyst with exchanging the electrolyte solution
between K-Ci and K-Pi by transmission mode at BL3U
in the UVSOR synchrotron. The electrolyte aqueous
solution of potassium carbonate was measured as
reference compounds.
[1] K. S. Joya, Y. F. Joya, and H. J. M. de Groot, Adv.
Energy Mater., 4 (9) (2014) 1301929.
[2] T. Shinagawa, M. T. Ng and K. Takanabe, Angew.
Chem. Int. Ed. Eng., 56 (18) (2017) 5061.
[3] A. C. Garcia, T. Touzalin, C. Nieuwland, N. Periniand M. T. M. Koper, Angew. Chem. Int. Ed. Eng., 58(37) (2019) 12999.

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Temperature Eﬀects on the X-ray Absorption Spectrum of Aqueous
Ca(NO3)2 Recorded at the Ca L-edge
D. Céolin1, T. Saisopa2, Y. Rattanachai2, H. Yuzawa3 and N. Kosugi3
1
Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, F-91192 Gif-sur-Yvette Cedex, France
Department of Applied Physics, Faculty of Sciences and Liberal Arts, Rajamangala University of Technology
Isan, Nakhon Ratchasima 30000, Thailand
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

2

Calcium dication is frequently studied due to its
abundance in human body and its importance inbiological processes. Thus, its local structure
determination is the subject of number of investigations,both experimental (XRD, EXAFS, MD, etc.) andtheoretical (QM/MM, MD). In aqueous solutions,
X-ray absorption spectroscopy (XAS) was used toprobe the eﬀect of the concentration on e.g., thehydration number, but the influence of the temperature
was not investigated, despite some information wasreported on other techniques [1].
In this context, we performed XAS measurements at
the BL3U beamline on aqueous Ca(NO3)2∙4H2O, using
the liquid cell in transmission mode. The setup oﬀers
the possibility to monitor its temperature (T). We
choose a high concentration close to the solubility limitof this salt in water at 0°C, that is 1050 g/L. The results
are presented in the Figure 1. Each spectrum has its
background removed.
A full attribution of the diﬀerent structures was given
in a previous paper [2]. The 2p-1 spin-orbit contributions
are located below (above) ~351 eV for L3 (L2),respectively. The temperature change from 0 to 60°C
do not influence the splitting between the two mainlines, nor the position of the smaller peaks. The intensity
ratio between peaks 1 and 2, which gives informationon the crystal field 10Dq value, is small. Despite weobserve a slight modification of this ratio with T, we
consider it as not relevant as it does not follow the Tvariation and is attributed to the background removal
procedure.
A more precise analysis shows a slight blue-shift of
the right side of the peaks toward the high photon
energies following the temperature increase (see insert
in Fig. 1 corresponding to a zoom of the main L3 line),
whereas the low energy sides remain quasi-unchanged.
The width of peak 1 for each T is shown in Fig. 2. The
photon bandwidth and the detector contribution are
constant and lead to an experimental resolution of 166
meV, whereas the Lorentzian broadening contribution
shows a slight increase roughly from 200 to 250 meV
within the T going from 0 to 60°C.
Temperature eﬀects were already probed by XAS inelectrolyte aqueous solutions at the O K-edge. For a 5
M LiCl aqueous solution [3], a redshift of the pre-edge
resonance maximum was observed when T increases. It
was attributed to the change of the distance between thebulk water molecules with T, whereas molecules in thefirst hydration shell of lithium ion are more strongly
bonded to it and less sensitive to T variations. In thepresent case, the sample concentration is high and close
to the solubility limit at 0°C. We can argue that thermal
motion at low T is reduced and slightly increases in thisT range. These observations should be confirmed bycomplementary measurements.

Fig. 1. X-ray absorption spectra of a 4.5 M Ca(NO3)2∙4(H2O)
aqueous solution, recorded in the vicinity of the Ca 2p
ionization threshold, for temperatures in the 0-60°C
range.

Fig. 2. Influence of temperature on the width of themain line (full width at half maximum: FWHM). The
Gaussian and Lorentzian contributions are extracted.
[1] A. A. Zavitsas, J. Phys. Chem. B, 109 (2005) 20636.
[2] T. Saisopa et al., J. Electron Spectrosc. Relat.
Phenom., 244 (2020) 146984.
[3] M. Nagasaka et al., J. Phys. Chem. B, 121 (2017)10957.

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Self-Assembled Hierarchical Nanosegregated Chiral Intermediate Phases
Composed of Two Diﬀerent Achiral Bent-Core Molecules
F. Araoka1, Y. Takanishi2, S-W. Choi3 and H. Iwayama4,5
1

RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
2
Faculty of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan3
Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University,
Yongin 17104, Republic of Korea
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki, Aichi 444-8585, Japan

Chirality is fascinating because of its fundamental
importance in nature. As we presented in the activity
report of the previous year, achiral BC molecules are
well-known for spontaneous chiral resolution at themacroscopic scale despite the chiral-carbon-atom-free(hence, achiral) molecules (Fig. 1a). The so-called B4phase—often the lowest temperature phase of BCs—isone such chiral mesophase in which a helicalnanofilament superstructure is spontaneously selfassembled. In this case, structural chirality, observed as
helical handedness, originates from the layered chiralityof tilted smectic layers twisting along the filaments.
Another very similar type of chiral phase formed byachiral bent-core molecules is the dark conglomerate(DC) phase. The DC also exhibits optically resolved
domains with strong optical activity, but it looks moreisotropic. The fundamental morphology of DCs
comprises disordered sponge-like structures of tilted
smectic layers. Although sponge-like structures do nothave morphological chirality, it is understood that theobserved macroscopic optical activity is attributed to
the layered chirality of the tilted smectic layers.
Recently, we explored some interesting chiralityrelated phenomena in nano-separated intermediatephases composed of two achiral bent-core liquid
crystalline molecules, one of which is circularly
polarized luminescence (CPL) in the nano-separated
intermediate phase blended with a luminescent dye [1].
Following up this work, we further extended thisconcept to realize dual-chiral intermediate phase (asillustrated in the right panel of Fig. 1a) of coexisting B4
and DC phases, using nanophase segregation between
two bent-core molecules and hierarchical selforganization.
Interestingly,
theluminescencedissymmetry factor of CPL from the nano-separated
dual-chiral phase of the B4 and DC was one order ofmagnitude higher than that of the previously reported
chiral phases of the bent-core system [2].
Thus, the present dual-chiral phase system looks
promising. However, its structure has not yet been
confirmed. Since the system is consisting of two
mesophases, direct observation methods such as usingtransmission electron microscope aren’t usable.

Therefore, for this sake, we performed resonant soft
X-ray scattering (RSoXS) experiment to identify thenano-separated phases. Our RSoXS setup was preparedin BL3U of UVSOR at IMS – A homemade vacuum
chamber equipped with a cooled CCD camera (Newton,
Andor) was used for small angle detection (2θ~1-15˚).
In the present study, the X-ray photon energy waschosen as 284.5 eV, corresponding to the carbon K-edge
absorption of the present sample mixtures. The sample
mixture was sandwiched between two SiN membranefilms and then sealed not to exposed to vacuum. The
sample chamber also equips a furnace to heat up thesample.
The RSoXS profile of the dual chiral phase (Fig. 1b)
was compared with those of the only-B4 (Fig. 1c) andonly-DC (Fig. 1d) phases. The RSoXS result clearlyshows that the patterns of two chiral phases aresuperimposed in the dual chiral phase. In addition, we
carefully examined the dual chiral phase with circulardichroism spectroscopy, polarizing light microscopy,
and diﬀerential scanning calorimetry, we concluded
that the model proposed in Fig. 1a is reasonable in thepresent dual chiral system.

Fig. 1. (a) Schematics of the nanoscopic structures of
the B4 and DC phases, and the nano-separated dualchiral phase. (b, c, d) RSoXS patterns obtained for (b)B4, (c), DC, and (d) dual chiral phases. [2][1] Kim et al. Adv. Funct. Mater. 29 (2019) 1903246.
[2] Lee et al. Int. J. Mol. Sci. 23 (2022) 14629.

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X-ray Absorption Spectra of Metal Carbonyl Solutions
T. Sasaki and H Xu
Department of Complexity Science and Engineering, Graduate School of Frontier Sciences,
The University of Tokyo, Kashiwa 277-8561, Japan

XAS measurements for liquid samples have beenenabled at UVSOR BL3U, giving new insights forphysicochemical properties of materials [1]. We havestudied O-K edge XAS measurements for cellobiose
aqueous solutions and found that XAS signals can be
simulated with CP2K and hydrogen bonding with watermolecules aﬀect the relative intensity of XAS peaks. In
this study metal carbonyl solutions were examined for
XAS measurements to gain information of metal
carbonyls dissolved in liquid phase, since metal
carbonyls can be regarded as good models for bothhomogeneous and heterogeneous catalysts. Therefore
we can expect XAS method will act as a new
characterization tool for chemical and catalytic
processes in liquid phase. In this study Mo(CO)6 andRu3(CO)12 were chosen as target molecules.
XAS measurements for liquid samples wereconducted at UVSOR BL3U using facilities developed
by Nagasaka et al. [1]. The liquid sample cell with
Si3N4 membranes was adopted, where the thickness of
the liquid layer was controlled by the He gas pressurearound the cell.
Fig. 1 shows O-K XAS spectrum for Mo(CO)6 (40mg) in 10 ml CH3CN at room temperature.
Concentration is 15 mM. This condition is close to thesaturated solution. A sharp peak at 531.25 eV wasobserved and can be attributed to excitation to C=O
1π* level. Broad features above 534 eV can beassociated with sigma bonding of C-O ligand.
Fig. 2 shows O-K XAS spectrum for Ru3(CO)12 (3mg) in 5 ml CHCl3 at room temperature. Concentration
is 0.94 mM. This condition is also close to the saturated
solution. It is noticed that peak intensity for Fig. 2 isweaker than that for Fig. 1, because of the low solubilityof Ru3(CO)12. A peak was found at 531.65 eV and canbe attributed to excitation to C=O 1π* level. Broadfeatures above 534 eV can be associated with sigma
bonding of C-O ligand.
Due to the limitation of rather low concentration C-K
edge measurements are diﬃcult since overlap withabsorption peaks by solvent molecules aﬀect the peaks
associated with CO ligand.
For the precise peak assignments MD calculation for
carbonyl species dissolved in solvent molecules andcore excitation simulation are now in progress. It is
expected to conduct measurements of other metal
carbonyls and observation of ligand exchange. Whether
site discrimination, for example atop coordination andbridging coordination is possible or not is alsointeresting point to be clarified.

Fig. 1. O-K XAS spectrum for Mo(CO)6 (40 mg) in 10
ml CH3CN at room temperature.

Fig. 2. O-K XAS spectrum for Ru3(CO)12 (5 mg) in 5
ml CHCl3 at room temperature.
[1] M. Nagasaka et al., J. Electrosc. Relat. Phenom.
200 (2015) 293.
[2] D. Akazawa et al., J. Chem. Phys. 156 (2022)
044202.

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Soft X-ray Absorption of Photocatalysts for Artificial Photosynthesis:
Ultraviolet Light Irradiation in Water
H. Onishi1,2, Yi Hao Chew1, K. Matsui1, N. Ichikuni3 and T. Yoshida4
1
School of Science, Kobe University, Kobe 657-8501, Japan
Division of Advanced Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Graduate School of Engineering, Chiba University, Chiba 263-8522, Japan
4
Reserch Center for Artificial Photosynthesis, Osaka Metropolitan University, Osaka 558-8585, Japan
2

Sodium tantalate (NaTaO3) and strontium titanate(SrTiO3) provide a class of semiconductor photocatalysts
which produce hydrogen–oxygen mixed bubbles in theoverall water splitting reaction, when properly dopedwith metal cations [1, 2]. We are conducting a series ofstudies to answer the question of why doping withmetal cations raised the quantum yield of the reaction[3]. Here, soft X-ray absorption is applied forcharacterizing the electronic structure of thephotocatalysts in the presence and absence of ultraviolet(UV) light for bandgap excitation.
NaTaO3 particles doped with Sr cations (2 mol%)were prepared through a solid-state reaction, andcharacterized with EDX and XRD in Kobe University.
The particles were suspended with water (5 g l-1) andsent to a liquid film cell for transmission absorption bya syringe pump (Figure 1). To avoid sedimentation of
the particles, pH of the suspension was tuned at 13, farfrom isoelectric point of the particles.
An Hg–Xe lamp (200 W) was used to irradiate UV
light for photocatalyst excitation. The photodiodedetecting transmitted X-ray was capped with a nickel
filter to minimize stray UV light from the lamp andhigher-order X-ray passing through the monochromator.
Figure 2 shows an oxygen K edge absorption
spectrum of Sr-doped NaTaO3 photocatalyst particles
suspended in water. It was not straightforward to placea significant amount of the photocatalyst particles in
the water film pinched with two SiN membranes. An

absorption band appeared at 531.5 eV was ascribed tothe photocatalyst particles but to be further examined,
since the oxidized layer of the membranes may provide
an absorption band at 530–531 eV.
Purin Sathirathai, an undergraduate student ofSirindhorn International Institute of Technology,
Thammasat University in Thailand, assisted us inphotocatalyst preparation under Sakura Science
Exchange Program by Japan Science and Technology
Agency. This study was supported by JSPS KAKENHI(grant numbers 18KK0161 and 22H00344).

Fig. 2. Oxygen K edge absorption spectrum of NaTaO3
photocatalyst particles doped with Sr cations observedin water without UV light irradiation. The absorbance
spectrum is shown in an arbitrary unit as a function of
X-ray energy.

Fig. 1.
Strontium-doped NaTaO3 photocatalyst
particles suspended in water. White suspension in thesyringe was sent to the liquid film cell for transmission
XAFS measurements.

[1] H. Kato, K. Asakura, A. Kudo, J. Am. Chem. Soc.
125 (2003) 3082.
[2] T. Takata, J. Jiang, Y. Sakata, M. Nakabayashi, N.
Shibata, V. Nandal, K. Seki, T. Hisatomi, K. Domen,
Nature 581 (2020) 411.
[3] H. Onishi, ChemSusChem 12 (2019) 1825.

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Hydration of Dimethyl Sulfoxide Probed by Liquid-Phase Soft X-ray
Absorption Spectroscopy
C. Sugahara1, K. Okada1 and H. Iwayama2,3
1

Graduate School of Advanced Science and Engineering, Hiroshima University,
Higashi-Hiroshima 739-8526, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan

Soft X-ray absorption spectroscopy oﬀers informationon the local atomic environment of a molecular system
under study by the resonant excitation of the local site.
Diﬀerent characters of water in solution, i.e. bulk andhydrated water, can be detected by the spectroscopy.
The subtle diﬀerences in character, however, prevent us
from clear distinction from one another without a useful
analysis method. We have proposed a new quantity,
called the excess absorption coeﬃcient, for the analysis
of absorption spectra of solutions and applied to theacetone–water binary system [1]. The analysis gives a
successful extraction of the hydrated component.
This study is intended for generalization by theapplication of the method to another solution. The
system of interest for this purpose is dimethyl sulfoxide(DMSO) aqueous solution. The DMSO molecule ismore polarized than acetone. This is shown by thediﬀerence in the values of excess molar enthalpy. The
acetone–water mixture has negative values only in the
dilute region [2], while the DMSO–water mixture has
negative values at all fractions and has greater absolutevalues [3]. We expect that more intensity in theabsorption component of hydrated water for the lattermixture.
The experiments were performed on the soft X-ray
beamline, BL3U. The photoabsorption spectra were
measured in the oxygen K-edge region, with sample
cell windows made of silicon nitride with a thickness of
150 nm. The incident photon energy was calibrated tothe peak at 530.88 eV of a polymer film [4]. The
absorption coeﬃcient was evaluated so as to match thevalue at 547.85 eV to that tabulated in the database [5].
The sample solutions were prepared by mixing liquid
DMSO with purified water to give the molar fraction of
DMSO, xD, in the range 0–0.35.
Observed absorption spectra of DMSO aqueous
solutions are shown in Fig. 1. The spectrum for pure
DMSO (xD = 1) has peaks at 532.6 and 534.0 eV. The
former peak, assigned to the π* ← O 1s transition of
DMSO, is clearly dependent on xD. The 4a1 ← O 1s
absorption peak of water at 534.7 eV seems to shift tolower energies with xD. The behavior is, however, notconclusive due to the overlap with the hump at about

534 eV which is assigned to another resonancetransition of DMSO. This fact indicates that in thissystem the distinction of hydrated water from the bulk
water requires a physicochemical analysis method: The
system is a perfect system for testing our method ofanalysis. The results of the analysis will be publishedelsewhere.

Fig. 1. The soft X-ray absorption spectra of liquidwater and DMSO aqueous solutions measured for aseries of molar fractions of DMSO. The spectrum of
the liquid DMSO is also shown for comparison.
[1] K. Okada, C. Sugahara, H. Iwayama and M.
Nagasaka, UVSOR Activity Report 2021, 49 (2022)
117.
[2] B. Löwen and S. Schulz, Thermochim. Acta 262(1995) 69.
[3] T. Kimura and S. Takagi, Netsu Sokutei 13 (1986)
2.
[4] M. Nagasaka, H. Yuzawa, T. Horigome and N.
Kosugi, J. Elec. Spectrosc. Relat. Phenom. 224 (2018)93.
[5] C. T. Chantler et al., NIST Standard Reference
Database 66 (1995; last update in 2005), available athttps://www.nist.gov/pml/x-ray-form-factorattenuation-and-scattering-tables.

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Multielectron-ion Coincidence Spectroscopy of I 4d inner-shell
Photoionization of CH3I and CH2I2 Molecules
M. Fushitani 1, Y. Hikosaka 2 and A. Hishikawa1,3
1
Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8602, Japan
Institute of Liberal Arts and Sciences, University of Toyama, 2630 Sugitani, Toyama, Toyama, 930-0194, Japan
3
Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8602, Japan
2

Inner-shell photoionization of molecules often leads
to formation of highly charged states followed byfragmentation processes. Identifying which ion species
are generated from which electronic states is of great
importance for the basic understanding of ultrafast
processes associated with inner-shell ionization.
Amongothers,multielectron-ion
coincidence
spectroscopy using a magnetic bottle type electron
spectrometer is a powerful approach to obtain suchinformation [1-3]. Here, we applied it to I 4d innershell ionization of CH3I and CH2I2 molecules toinvestigate fragmentation processes occurring fromdoubly charged states.
Electrons generated by photoionization with asynchrotron radiation at 100 eV were guided from theinteraction region into a time-of-flight (TOF) tube (1.5m) by magnetic fields from a permanent magnet andsolenoid coil while ions were pushed into the tube by
applying pulsed voltages to ion-collecting electrodes[1]. These electrons and ions were detected by amicrochannel plate placed on the opposite side of the
TOF tube.
Figure 1 shows Auger electron spectra obtained incoincidence with I 4d photoelectrons, I+ ions andselected counterpart ions for (a) CH3I and (b) CH2I2.
These Auger peaks provide information on the locationof excited electronic states producing the fragment ion
pairs. In Fig.1(a), the pair of I+ and CH3+ ions are mainly
generated together with Auger electrons having kinetic
energies around 20-30 eV which correspond to doubly
charged states associated with outer-valence
configurations [4,5]. On the other hand, Auger signals
are observed below 20 eV for the (I+, CH2+), (I+, CH+),and (I+, C+) ion pairs, showing that these ion pairs areformed preferentially from higher excited states related
to inner-valence configurations [4].
In the case of CH2I2 (Fig.1(b)), the (I+, CHnI+) ion pairreflecting the single C-I bond cleavage is produced
mostly with Auger electrons having 25-32 eV kinetic
energies. By contrast, Auger signals appear in the lower
energy region for other ion pairs associated with two
C-I bond fissions, indicating the dissociations occur in
excited doubly charged states.
The present study shows a promising approach forapplications and fundamental understanding of
nonlinear inner-shell ionization of iodine-containing
molecules by intense free-electron lasers.

Fig. 1. PEPEPIPICO spectra of I 4d inner-shell
photoionization at 100 eV for (a) CH3I and (b) CH2I2.
[1] Y. Hikosaka, J. Electron Spectrosc. Rel. Phenom.
255 (2022) 147158.
[2] Y. Hikosaka and E. Shigemasa, Int. J. Mass
Spectrom. 439 (2019) 13.
[3] M. Fushitani et al., Phys. Rev. A (Letter) 107 (2023)
L021101.
[4] A. Hult Roos et al., Chem. Phys. 491 (2017) 42.
[5] A. Bodi et al., Phys. Chem. Chem. Phys. 25 (2023)
7383.

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BL4B

Quadruple Auger Decay from Xe 4s Core-Hole State Studied byMulti-Electron−Ion Coincidence Spectroscopy
Y. Hikosaka
Institute of Liberal Arts and Sciences, University of Toyama, Toyama 930-0194, Japan

Emissions of multiple Auger electrons, following
inner-shell photoionization of atoms in the soft X-ray
region, can occur within the permitted limits of theenergetics. Multi-electron coincidence spectroscopyusing a magnetic bottle electron spectrometer is a
powerful means for studying multiple Auger decay.
Discrimination of multiple Auger processes against
dominant single Auger decay can be improved byfiltering multi-electron coincidences with the additional
detection of product ions relevant to the multiple Auger
processes. By adding such ion detection capability to amagnetic bottle electron spectrometer, multi-electron−
ion coincidence measurements can be performed very
eﬃciently [1-3].
In this study, quadruple Auger decay of the Xe 4s
core-hole state is investigated by multi-electron−ion
coincidence spectroscopy with a magnetic bottle
electron spectrometer [4]. Figure 1(a) shows the total
electron spectrum (black curve) and the spectrum
filtered by coincidence with Xe5+ ions (red curve),
where the 4s photoelectron peak is observed around a
kinetic energy of 180 eV. From the net intensities of the4s peaks observed in the total and coincidence spectra,
the fraction of the quadruple Auger path in the 4s decay
was determined to be 16%.
The two-dimensional map in Fig. 1(b) displays thecorrelation between the fastest electron’s energy andthe sum of the energies of the other four electrons,
determined from the six-fold coincidence including
Xe5+ ion. It is possible to recognize structures running
diagonally. The diagonal structures correspond to theformation of Xe5+ levels, resulting from the energy
conservation (photon energy) - (binding energy of the
Xe5+ state) = (fastest electron’s energy) + (the sum of
the energies of the other four electrons). Enhancementof Xe5+ formation is observed at the 4s photoelectronenergy, corresponding to quadruple Auger decay fromthe 4s-1 state.
Figure 2 shows the Xe5+ distribution populated by thequadruple Auger decay from the 4s-1 state. The
distribution is obtained by integrating the coincidence
counts in Fig. 1(b) along the direction (fastest electron’senergy) + (the sum of the energies of the other fourelectrons) = const., where the fastest electrons wererestricted to be of the 4s photoelectron energy range. In
addition to the formation of the 5p-5 levels, both
histograms show substantial formation of excited Xe5+
levels. The final formation fractions of the 5p-5, 5s-15p-4,
and 5s-25p-3 levels by the quadruple Auger decay are
estimated to be 7%, 7% and 2% of the 4s decay,
respectively.

Fig. 1. (a) Inner shell photoelectron spectra of Xe
observed at a photon energy of 391.7 eV, obtained for
total events in the coincidence dataset (black) or byfiltering with the detection of a Xe5+ ion (red). (b) Twodimensional map showing the correlation between thefastest electron’s energy and the sum of the energies ofthe other four electrons.

Fig. 2. Xe5+ distribution populated by the quadruple
Auger decay from the 4s-1 state.
[1] Y. Hikosaka and E. Shigemasa, Int. J. Mass
Spectrom. 439 (2019) 13.
[2] Y, Hikosaka, J. Electron Spectrosc. Relat. Phenom.
255 (2022) 147158.
[3] Y. Hikosaka and S. Fritzsche, Phys. Chem. Chem.
Phys. 24, (2022) 17535.
[4] Y, Hikosaka, Phys. Rev. A 106 (2022) 062814.

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BL4B

Metastable OCS3+ States Investigated by Multi-Electron−Ion Coincidence
Spectroscopy
Y. Hikosaka
Institute of Liberal Arts and Sciences, University of Toyama, Toyama 930-0194, Japan

Triply charged molecular ions are always
energetically unstable due to Coulomb repulsion
between the three positive charges. However, low-lying
trication states in some limited molecules are known to
be stable for more than μs due to the presence of deep
minima on the potential energy surfaces. In this study,
metastability of OCS3+ states populated by the S 2p
double Auger decay has been investigated by multielectron−ion coincidence spectroscopy. A magnetic
bottle electron spectrometer with ion detection
capability [1-4] was employed for this investigation,and the high detection eﬃciencies for electrons enabled
to derive the information of stability of OCS3+ electronic
states.
The double Auger decay of the S2p-1 states in OCS
can be isolated by inspecting electron triple coincidences
including a S2p photoelectron. The two-dimensional
map in Fig. 1 is derived from the electron triple
coincidences, displaying the energy correlation
between the two electrons other than the S2p
photoelectron. On this map, several diagonal stripes are
identified in (faster electron’s energy) + (slower
electron’s energy) =95-115 eV, which are formed bydouble Auger decay. The population of the OCS3+ states
formed by the S2p double Auger decay is revealed byprojecting the coincidence yields on the diagonal axisof (faster electron’s energy) = (slower electron’senergy). The resultant OCS3+ spectrum is shown in Fig.
2 as black curve. Several peaks are observed in the
kinetic energy range of 95-115 eV, corresponding to the
diagonal structures seen on the two-dimensional map in
Fig. 1. Moreover, a broad structure is seen in thebinding energy range of 80-95 eV. These spectral
profiles agree with the previous investigation by Elandet al. [5].
Metastability of OCS3+ states can be investigated byinspecting the ion species detected in further
coincidence with S2p photoelectron and two Auger
electrons. The double Auger spectrum filtered byfurther coincidence with parent OCS3+ ion is presented
in Fig. 2 as red shaded spectrum. Only the peak for the
ground 3π-3 2Π state at a binding energy of 60 eV isexhibited in the spectrum, revealing that the groundstate is metastable in the μs regime. An MRCI/CASSCF
calculation [5] predicts the ground 3π-3 2Π state has apotential surface with a potential well along both
directions lengthening the CS and CO bonds, although
excited OCS3+ states are all unbound to lengthening the

CS bond. The present observation is in consistent withthe calculation results.

Fig. 1. Two-dimensional map showing the energy
correlations between two Auger electrons emitted in
the S 2p double Auger decay of OCS, which wasderived from electron triple coincidence.

Fig. 2. OCS3+ spectra formed by the S2p double Auger
decay of OCS: total spectrum (black solid curve) andthe one filtered with further coincidence with parent
OCS3+ ions (red shaded spectrum).
[1] Y. Hikosaka and E. Shigemasa, Int. J. Mass
Spectrom. 439 (2019) 13.
[2] Y, Hikosaka, J. Electron Spectrosc. Relat. Phenom.
255 (2022) 147158.
[3] Y. Hikosaka and S. Fritzsche, Phys. Chem. Chem.
Phys. 24, (2022) 17535.
[4] Y, Hikosaka, Phys. Rev. A 106 (2022) 062814.
[5] J.H.D. Eland et. al, J. Chem. Phys. 132 (2010)014311.

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Ⅲ-3 Chemistry

BL4B

Soft X-ray Absorption Study of Semiconductor Photocatalysts for HighlyEﬃcient Oxidation of Water
T. Yoshida1, N. Ichikuni2, H. Onishi3,4 and Yi Hao Chew3
1

Reserch Center for Artificial Photosynthesis, Osaka Metropolitan University, Osaka 558-8585, Japan
2
Graduate School of Engineering, Chiba University, Chiba 263-8522, Japan3
School of Science, Kobe University, Kobe 657-8501, Japan
4
Division of Advanced Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan

A number of metal oxides including gallium oxide,(Ga2O3), sodium tantalate (NaTaO3) and strontium
titanate (SrTiO3) provide a class of semiconductor
photocatalysts highly eﬃcient for the overall water
splitting reaction, when properly doped with foreign
metal cations. [1-3]. We are conducting a series ofstudies to answer the question of why metal-cation
doping raised the quantum yield of the reaction [4].
Here, soft X-ray absorption is applied for characterizing
the electronic structure of the photocatalysts in thepresence and absence of ultraviolet (UV) light forbandgap excitation.
Sub-micrometer-sized Ga2O3 particles were preparedin Osaka Metropolitan University, while NaTaO3 dopedwith Sr2+ cations and SrTiO3 doped with Al3+ cations
were prepared in Kobe University. Oxygen K edge
absorption spectrum of the photocatalysts particles wasobserved under vacuum in the presence and absence of
UV light provided by a Hg–Xe lamp (200 W).
In XAFS measurement of oxygen K edge, thephotocatalyst particles were molded as disks of 7-mm
diameter. The disks were placed in a vacuum chamber,
irradiated with incident X-ray, and fluorescent X-ray
was detected with a silicon drift detector (SDD). The
detector was capped with a 150-nm-thick aluminum
film (LUXEL, TF110) to minimize contribution ofstray UV light to detector response (Fig. 1).
Figure 2 shows a set of oxygen K edge spectra
observed on Sr-doped NaTaO3 photocatalyst disk. The
low energy band, which was assigned to the electronictransition from the oxygen 1s to oxygen 2p levels
hybridized with tantalum 5d orbitals, appeared at 531.2

eV in the absence of UV light irradiation. The band
shifted by 0.4 eV to the low-energy side under UV
irradiation.
A possible reason of the band shift is the conduction
band partially filled with bandgap-excited electrons.
The density of vacant states, the final states of the Kedge absorption, should have modified with theelectrons excited from the valence band. The oxidation
state of Ta cations decreased from 5+ to 4+ by the
bandgap excitation.
This study was supported by JSPS KAKENHI (grant
numbers 18KK0161 and 22H00344).

Fig. 2. Oxygen K edge absorption spectrum of a Srdoped NaTaO3 photocatalyst disk in the absence (upper
panel) and presence (lower panel) of UV-lightirradiation.

Fig. 1. A devise capping the SDD with the aluminum
filter for fluorescence yield detection of oxygen K edge
absorption spectrum under UV-light irradiation.

[1] Y. Sakata, T. Hayashi, R. Yasunaga, N. Yanaga, H.
Imamura, Chem. Commun. 51 (2015) 12935.
[2] H. Kato, K. Asakura, A. Kudo, J. Am. Chem. Soc.
125 (2003) 3082.
[3] T. Takata, J. Jiang, Y. Sakata, M. Nakabayashi, N.
Shibata, V. Nandal, K. Seki, T. Hisatomi, K. Domen,
Nature 581 (2020) 411.
[4] H. Onishi, ChemSusChem 12 (2019) 1825.

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BL7B

High-Resolution Photoelectron Spectroscopy of Unexplored Chiral Systems
for Demonstration of the Photoelectron Circular Dichroism
H. Kohguchi1, Y. Hikosaka2, T. Kaneyasu3, S. Wada1 and Y-I. Suzuki4
1

Graduate School of Advanced Science and Engineering, Hiroshima University,
Higashi-Hiroshima 739-8526, Japan
2
Institute of Liberal Arts and Sciences, University of Toyama, Toyama 930-0194, Japan
3
SAGA Light Source, Tosu 841-0005, Japan
4
School of Medical Technology, Health Sciences University of Hokkaido, Tobetsu, 061-0293, Japan

Photoelectron circular dichroism (PECD) has
attracted attention as a novel molecular chirality
detection method. One of the remarkable attributes of
PECD is that the asymmetric photoelectron angular
distribution is generated from isotropically oriented
molecules in the gas phase. In addition, PECD depends
on the final ionic states so that the PECD data can be
related to the chirality of the molecular orbitals. We
have been conducting state-resolved PECD
measurements with the UVSOR BL1U beam line.
Although the circularly polarized light supplied by the
BL1U undulator is indispensable for detecting thestate-dependence of PECD [1], the narrower photon
energy spread is desired for resolving the electronic
structure of the observed photoelectron spectra. The
width of the experimental photoelectron spectra islimited by our VMI apparatus as well as the lightsource. High-resolution photoelectron spectra provide
unambiguous assignment of the electronic states which
is applicable to the PECD image data. For combining
the narrow band spectra with the PECD results
measured in BL1U, we have developed the VMI
apparatus and inspected the performance in the BL7B
beam line.
We adopt two types of imaging systems in our VMI
apparatus employs: a resistive anode and a CCD
camera. The total resolution was evaluated inmeasurement of Ar photoelectron images in BL7B. The
photoelectron images measured with the resistive
anode imager exhibited suﬃciently high resolution thatthe spin-orbit dual ring was resolved, as shown in Fig.
1 (a)-(d). The same measurement with the camera
system yielded the image data with a comparable
resolution but with a poor signal-to-noise ratio (Fig. 1(A)-(D)). This is because the numerical operation
determining the photoelectron positions of the camera
system was found to be less eﬃcient by 10 % of theresistive anode imager. The performance of these two
imaging systems was directly examined with thenarrow band light source, providing necessary
improvement toward the state-resolved PECD
measurements.
The photoionization experiments of chiral compoundswith a heat nozzle were conducted as another evaluationof the machine developments. An increase of thephotoelectron in a particular photon energy region wasmeasured with the elevated nozzle temperature, which
was ascribed to the vaporized chiral molecules (Fig. 2).
The photoelectron emitted in the shorter wavelengththan 100 nm was regarded to be due to contaminatedwater, which is generally hard to eliminate. This result
indicates that the density of the vapor in the irradiation
volume needed to be increased for the state-resolved
PECD measurements of new chiral systems. The
machine developments should be reconsidered basedon the results of the BL7B measurements.

Fig. 1. Photoelectron images of Ar measured at various
photon energy from 75 nm to 50 nm; (a)-(d) with aresistive anode imager, (A)-(D) with a CCD camera
capturing a phosphor screen image.

Fig. 2. Photoelectron yield spectrum of binaphthol atvarious nozzle temperatures near the ionizationthreshold.
[1] H. Kohguchi, Y. Hikosaka, T. Kaneyasu, S. Wada,
H. Ota, M. Fujimoto, M. Kato and Y-I. Suzuki, UVSOR
Activity Report 48 (2020) 93.

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Ⅲ-3 Chemistry

BL7B

The Challenge of Photoionization Plasma Generation Using Synchrotron
Radiation Source for Study of Plasmas in Interstellar Space and in Nuclear
Fusion Devices
M. Kobayashi1, H. Iwayama2, J. Takahashi3, S. Yoshimura1, H. Ota2, K. Kobayashi3,
M. Katoh2,4, H. Nakamura1, I. Sakon5, K. Sawada6 and Y. Kebukawa3
1

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Myodaiji,Okazaki 444-8585, Japan
3
Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku,Yokohama 240-8501, Japan
4
Hiroshima Synchrotron Radiation Center, Hiroshima University, 739-0046, Japan
5
Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
6
Graduate School of Engineering, Shinshu University, Nagano, Japan2

An interstellar space is filled with interstellar plasmas,
which is generated by ionization by cosmic rays or byinterstellar radiation field [1]. In nuclear fusion devices[2], it is considered that neutral atoms and molecules inthe divertor region are photoionized by a light comingfrom the confinement region and the scrap-oﬀ layers,
where hot plasmas emit light in various energy ranges,
from EUV through visible to infrared ranges.
Characteristics and roles of the photoionized plasmas
are, however, not yet fully understood: What is thedependency of the density and temperature of thephotoionized plasmas on the energy range of the light?
How the plasma transport under an influence of space
magnetic field aﬀects chemical evolution of organic
molecules in the interstellar space? How thephotoionization process aﬀects the atomic/molecular
processes in the divertor region of the nuclear fusion
devices, which plays important roles on a device wallheat load mitigation?
To address these issues, we attempt to generate
photoionized plasmas by using the Synchrotron
Radiation Source UVSOR-III. There has been
substantial works on the photoionization by using laser
light with relatively high power source. In the present
work, however, we are interested in photoionization by
the radiation field (continuum light) in order to mimic
the interstellar radiation field and the radiation in thefusion devices, such as Bremsstrahlung. It is expectedthat the photoionization by the continuum light issignificantly diﬀerent from those by the laser, becauseof the continuous energy distribution that can excite
and ionize at various energy levels simultaneously.
The beamline BL7B is used to generate a continuum
light from 30 to 400 nm with 0th order emission. A gas
cell has been installed inside the irradiation chamber tomaintain high pressure of the sample gas while keeping
a good vacuum condition for the beamline. A high gaspressure is necessary to enhance the photoionization
events through an interaction between the photons andneutral atoms/molecules. Fig.1 shows the gas cell basedon a ICF34 cube. Holes of diameter of 1 to 2 mm are
made for the injection of the light into the cell as well
as for a gas outlet. Optical fibers are installed at the gas

cell for measurements of spectra of VUV, visible andmid infrared range from the photoionized plasmas. The
gas is fed to the cell through the pipe at the top of thecell. An electrode is situated at the bottom of the celland is biased up to +30V with respect to the ground tomeasure electron saturation currents of the plasmas.
As a sample gas, Ar and hydrogen were introduced
respectively. The ionization potentials of the gaseousare 14.5 and 13.6 eV, respectively. The light from theBL7B beamline has a peak intensity at around 50 nm,
which corresponds to a photon energy of 24.8 eV. The
gas pressure inside the gas cell could be increased to anorder of 1 Pa while the ambient pressure outside of thecell was kept at an order of 10-4 Pa and the pressure at
the upstream of the beamline was at an order of 10-6 Pa.
A beam of a few mm diameter could be injected into
the gas cell through the holes. The photon flux of thebeam was measured with a photodiode, and wasestimated at an order of 1011 photons/s/mm2. However,no significant signal of photoionization was obtained
this time. More challenges to come by optimizing thegas cell shape and the measurement system.

Fig. 1. A gas cell for the photoionization experiments.
[1] E.F.van Dishoeck et al., Faraday Discuss 133 (2006)
231.
[2] M. Kobayashi et al., Nucl. Fusion 62 (2022) 056006.

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