Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We investigated neutral species in the matrix-assisted laser desorption and ionization (MALDI) plume using femtosecond laser ionization spectrometry with simultaneous measurement of the standard MALDI spectrum of the identical MALDI event induced by pulsed UV laser irradiation. The ratio of neutral species in the plume [A](p)/[M](p) (A = phenylalanine (Phe) or alanine (Ala), M = 2,5-dihydroxybenzoic acid (DHB)) was confirmed to be the same as that of the sample mixture in the range of [A](0)/[M](0) = 4 x 10(-4)-1, indicating the validity of the widely adopted approximation [A](p)/[M](p) = [A](0)/[M](0) in the reaction quotient of the proton transfer reaction MH+ + A reversible arrow M + AH(+). An effective parameter representing the extent of thermal equilibrium in the thermal proton transfer model is introduced for the first time. Numerical simulation based on this semiequilibrium model successfully reproduced variations of MALDI signal intensities AH(+) and MH+ with two parameters: the fraction of ionized matrix a <= 10(-5) and an effective temperature T = 1200 and 1100 K for Phe/DHB and Ala/DHB systems, respectively. These values show good agreement with those determined previously by different experimental approaches. The extent of thermal equilibrium was determined to be 95% and 98% for Phe/DHB and Ala/DHB systems, respectively, suggesting that the proton transfer reactions almost proceed to their thermal equilibrium.

DOI： 10.1021/acs.jpca.6b09591

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Multi-electron coincidence spectroscopy using a magnetic-bottle electron spectrometer has been applied to the study of the Auger decay following Ols photoionization of condensed H2O molecules. Coincidence Auger spectra are obtained for three different photoelectron energy ranges. In addition, the energy distribution of the slow electrons ejected in the Auger decay of the Ols core hole is deduced from three-fold coincidences. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2016.10.006

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In the last five years, a strong experimental and theoretical activity has been dedicated to the study of inner-shell double photoionization. Almost simultaneously, between 2009 and 2011, different experiments were performed using two different light sources: well established third generation synchrotron light sources that exist for more than two decades and recently developed x-ray free electron lasers (X-FEL) that provide brightness of about 10 orders of magnitude higher. The high photon flux of X-FEL has made possible the successive absorption of many x-ray photons by inner-shell electrons in femtosecond timescale. The possibility to create multiple inner-shell vacancies with this new X-FEL light source has resuscitated "prophetic" 25 years old calculations by Cederbaum et al. [1,2] concerning double K-shell ionization that could be of great interest when conventional Electron Spectroscopy for Chemical Analysis (ESCA) finds some limitations. As a feedback, this has stimulated new theoretical developments. On the other hand, it was considered practically out of reach to observe such states with conventional third generation synchrotron light sources due to the very weak probability to eject two inner-shell electrons by a single photon when the dominant process, that could mask everything else, is single inner-shell ionization. However, due to the development of very efficient detection techniques, it was also possible to perform spectroscopy of double core-hole states with excellent accuracy using third generation synchrotron sources.
In this paper we give an outlook on the basis of recently published results, of the complementarity of these light sources for double core-hole spectroscopy. Some new developments and results are also presented with a prospective of what could be done in the future with the technical breakthrough that will be necessary to improve our further understanding of chemical analysis. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2015.06.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have studied the site-specific formation of metastable OCS2+ in the C1s and the O1s Auger decays of OCS molecules by using an Auger-electron-ion coincidence technique. The coincidence measurement reveals the metastable character of the Auger final states with the (3 pi)-2 configuration. The formation of metastable OCS2+ is observed negligibly in the C1s Auger decay and only weakly in the O1s Auger decay, in contrast to the favorable metastable formation previously reported for S2p Auger decay. It is found that the origin of the site-specificity in the formation of metastable OCS2+ arises from the localization effect of the valence orbital involved in the Auger transition. The dissociative dication states related to individual fragmentation pathways are also derived from the coincidence measurement.

DOI： 10.1088/0953-4075/48/12/125101

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_491

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We have studied single photon double K-shell ionization of small molecules (N-2, CO, C2H2n, (n = 1-3),...) and the Auger decay of the resulting double core hole (DCH) molecular ions thanks to multi-electron coincidence spectroscopy using a magnetic bottle time-of-flight spectrometer. The relative cross-sections for single-site (K-2) and two-site (K-1K-1) double K-shell ionization with respect to single K-shell (K-1) ionization have been measured that gives important information on the mechanisms of single photon double ionization. The spectroscopy of two-site (K-1K-1) DCH states in the C2H2n (n = 1-3) series shows important chemical shifts due to a strong dependence on the C-C bond length. In addition, the complete cascade Auger decay following single site (K-2) ionization has been obtained. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2013.10.002

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Ultrafast dissociation of the HCl and HBr molecules excited respectively to the 2p(3/2) -> sigma* and 3d(5/2) -> sigma* resonances are studied with high resolution photoelectron spectroscopy. Sharp vibrational molecular lines and broad atomic lines are observed. The analysis of the profile of the atomic lines gives access to the lifetimes of the inner shell 2p(3/2) hole in the Cl* (2p(3/2))(-1) 3s(2)3p(6) configuration, and the inner shell 3d(5/2) hole in the Br* (3d(5/2))(-1) 4s(2)4p(6) configuration. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2014.06.006

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An Auger-electron-ion coincidence method is applied to study the site-specific formation of metastable CO22+ in the C1s and O1s Auger decays of CO2. It is found that only dication states with the electronic configuration of 1 pi(-2)(g) are relevant to the metastable formation. These dication states are favorably produced in the O1s Auger decay, because of the charge distribution of the 1 pi(g) orbital localizing at the O site. Fragmentation channels of dissociative CO22+ states are also investigated. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2014.04.030

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Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/1742-6596/488/2/022013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The energy resolution and the detection efficiency of a magnetic bottle electron spectrometer equipped with an electrostatic retarder are examined, with a particular focus on its application to electron coincidence measurements. The electrostatic retardation properly improves the energy resolving power of the spectrometer. No significant decrease in detection efficiency is observed when retardation voltages are applied. Photoelectron-Auger electron coincidence measurement of the L2,3VV Auger decay in CS2 is performed by using the magnetic bottle spectrometer, which reveals Auger transition intensities varying for the different core holes. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2014.01.017

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have observed single photon one-site (K-2) and two-sites (K-1K-1) double K-shell ionization in C2H2n (n-1-3) sequence and in isoelectronic C2H2. N-2 and CO molecules. The spectroscopy of K-1K-1 states is much more sensitive to the bond length than conventional ESCA spectroscopy based on single K-shell ionization. The mechanism of single photon two-sites is due to a knock-out process in which a primary photoionized 1s electrons eject another Is electron on the neighbor atom.

DOI： 10.1088/1742-6596/488/2/022013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Electron reemission following photoelectron recapture due to post-collision interaction has been studied at 0.7 eV the inner-shell photoionization threshold of water molecules, using a multi-electron coincidence method. Electron reemissions after single Auger decay occur from O and OH fragments which are produced by the dissociations of high-n Rydberg H2O+ states populated through photoelectron recapture. In addition, electron reemissions after double Auger decay are identified in triple coincidence events, where autoionization lines from O and O+ fragments are observed. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4808028

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have observed single photon double K-shell photoionization in the C2H2n (n = 1-3) hydrocarbon sequence and in N-2 and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K-2 process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K-1K-1 process). In the C2H2n sequence, the spectroscopy of K-1K-1 states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K-1K-1 double core ionization in the C2H2n sequence and in the isoelectronic C2H2, N-2 and CO molecules validates a knockout mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case. DOI: 10.1103/PhysRevLett.110.163001

DOI： 10.1103/PhysRevLett.110.163001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Double Auger decay of O1s(-1) and its satellite states in H2O has been studied with a multi-electron coincidence method, and a process leading to autoionizing O* fragments has been revealed. The breaking of the two O-H bonds producing the autoionizing O* fragments occurs for highly excited H2O2+ populated by the initial Auger decay. The O* fragments are more favorably produced in the decay from the satellite states, resulting from the larger population of highly excited H2O2+ states inheriting the valence excitation in the initial state. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768213]

DOI： 10.1063/1.4768213

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The Auger decay channels of the Ar 2p satellite states have been investigated using a multielectron coincidence technique, using a magnetic bottle time-of-flight electron spectrometer. For the Ar+(2p(-1)3p(-1)np) satellite states the 2p hole is filled first, while for the Ar+(2p(-1)3s(-1)4s) satellite states the 3s hole is filled first with leading to Ar2+(2p(-1)3p(-1)) states, which subsequently undergo an Auger decay leading to the filling of the 2p hole.

DOI： 10.1103/PhysRevA.85.043405

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Single photon double K-shell ionization of small molecules (N-2, O-2, CO, CO2) has been observed by coincidence detection of two photoelectrons with two Auger electron and reveals properties of hollow molecules.

DOI： 10.1088/1742-6596/388/2/022027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We observe the formation in a single-photon transition of two core holes, each at a different carbon atom of the C2H2 molecule. At a photon energy of 770.5 eV, the probability of this 2-site core double ionization amounts to 1.6 +/- 0.4% of the 1-site core double ionization. A simple theoretical model based on the knockout mechanism gives reasonable agreement with experiment. Spectroscopy and Auger decays of the associated double core hole states are also investigated.

DOI： 10.1103/PhysRevLett.107.193004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s2s(2)2p(4) configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

DOI： 10.1103/PhysRevLett.107.113005

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Cascade Auger electron emission following Xe 3d photoionization has been investigated using a multi-electron coincidence technique, which utilizes an electron spectrometer of magnetic bottle type. It has been found that the Xe2+ states of the 4p(-1)4d(-1) configuration, formed by the Auger decay of the Xe+ 3d(3/2,5/2)(-1) states, dominantly turn into triply charged states of the 4d(-2)5p(-1)/4d(-2)5s(-1) configurations. The Xe2+ 4s(-1)4d(-1) states, formed by the 3d Auger decay, yield the 4p(-1)4d(-1)5p(-1) states as well as the 4d(-3) states. From the coincidence spectrum among three Auger electrons, it is suggested that the Xe2+ 4p(-1)4d(-1) states give rise to the following cascade processes: 4p(-1)4d(-1) -> 4d(-2)5p(-1) -> 4d(-1)5p(-3).

DOI： 10.1088/0953-4075/44/7/075003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The formation of hollow molecules (with a completely empty K shell in one constituent atom) through single-photon core double ionization has been demonstrated using a sensitive magnetic bottle experimental technique combined with synchrotron radiation. Detailed properties are presented such as the spectroscopy, formation, and decay dynamics of the N-2(2+) K-2 main and satellite states and the strong chemical shifts of double K holes on an oxygen atom in CO, CO2, and O-2 molecules.

DOI： 10.1103/PhysRevLett.106.063003

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The absolute cross sections of single electron capture during the collision of N(2+) with He have been measured over the energy range 0.1-300 eV/u. From the plot showing the dependence of cross sections on energy, the following three remarkable observations can be made: (1) the cross sections exhibit an oscillatory structure below 1eV/u, (2) a bend in the cross sections appears at approximately I eV/u and (3) there is a dip in the cross sections at approximately 70 eV/u. The formation of an oscillatory structure is attributed to the glory effect. The bend in the cross sections occurs owing to the attractive potential part of a 1(2)Pi state of quasimolecule NHe(2+). The dip in the cross sections appears as a result of opening a new reaction path above 70eV/u. The glory effect can be observed for the first time on a total cross section even for slow ion-neutral collisions. The objective of this study is to explore the possibilities of providing a detailed explanation of energy dependence measurements in order to study reaction dynamics for a charge changing process.

DOI： 10.1088/1742-6596/163/1/012056

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have measured vibrationally-resolved molecular-frame photoelectron angular distributions (MF-PAD) from the C 1s level of CO molecules in the sigma shape resonance region. The MF-PAD's for vibrational levels (v(f) = 0, 1, and 2) in the C 1s --> epsilonlsigma channel are apparently different one from another at each incident photon energy. These experimental MF-PAD's agree with the present theoretical results from averaging the nuclear distance dependent dipole matrix elements with the relaxed core Hartree-Fock calculations. The results show that the MF-PAD's sensitively depend on the vibrational levels. This means that the internuclear distance dependences of phases and of magnitudes of dipole matrix elements play a crucial role in the C 1s photoionization of CO. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2004.02.043

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Differential cross sections have been measured for vibrationally elastic scattering of electrons from ozone molecules at incident electron energies from 2 eV to 10 eV in the angular range from 20degrees to 120degrees. Absolute values of the differential cross sections have been obtained by means of the relative flow method. Integral and momentum transfer cross sections have been derived from the measured data by extrapolating to 0degrees and 180degrees scattering angles. Comparison was made between the present measurements and those from other experiments and theoretical calculations.

DOI： 10.1143/JPSJ.73.892

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured with vibrational resolution. A strong dependence of the angular distributions on the vibrational states of the residual molecular ion has been found for the first time in the region of the shape resonance. Calculations in the relaxed core Hartree-Fock approximation have reproduced the angular distributions fairly well in the general shapes of the angular distributions due to the correct description of nuclear motion as an average of the internuclear-distance-dependent dipole amplitudes.

DOI： 10.1103/PhysRevLett.91.163001

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Angular distributions of photoelectrons (ADPs) from the 2sigma(g) shell of a fixed-in-space N(2) molecule have been measured for left- and right-elliptically polarized, as well as for linearly polarized, light. From these data a set of dipole matrix elements and phase shift differences characterizing the process has been determined taking into account the acceptance angles of both electron and ion detectors, i.e. the complete experiment has been performed. Good agreement between the experimental and the relevant theoretical values calculated in the random phase approximation is obtained. Based on the results of the complete experiment, three-dimensional ADPs and ions are predicted for different light polarizations.

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Helium double photoionization (gamma,2e) triple differential cross sections (TDCSs) were measured at an excess energy of 60 eV using a dual toroidal spectrometer and synchrotron radiation from a helical undulator (BL-28A, Photon Factory, Japan). Energy-sharing ratios (R=E-2/E-1) for the two ejected electrons of 5 and 11 are studied with both right- and left-handed elliptically polarized light. The TDCSs are found to be in good agreement with those obtained using the hyperspherical R matrix with semiclassical outgoing waves theory. The circular dichroism for a limited mutual angular range (phi(12)approximate to110degrees-200degrees) is determined from the experimental data for both R=5 and 11, and compared to theoretical calculations performed over the complete range of mutual angles. No dynamic nodes are found in either the experimental (within the explored phi(12) range) or theoretical circular dichroism for these R values at this excess energy.

DOI： 10.1103/PhysRevA.65.052717

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Angular distributions of photoelectrons from a 2sigma g shell of fixed-in-space N-2 molecules have been measured for left- and right-elliptically polarized and for linearly polarized light at several photon energies in the region of sigma* shape resonance. That allowed the determination of a set of dipole matrix elements and phase shift differences characterizing the process. These data clearly show the enhancement of the f sigma(u) partial cross section in the resonance simultaneously with an abrupt increase of the corresponding phase shift by pi, which is the first experimental demonstration of the nature of the sigma* shape resonance in homonuclear diatomic molecules.

DOI： 10.1103/PhysRevLett.88.063003

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Triple differential cross sections (TDCSs) of tile two ejected chiral electrons from helium were measured for several kinematic conditions using circularly polarized synchrotron radiation at tile Photon Factory. The selected kinematic conditions were E=9 eV (R=2,8), E=40 eV (R=7, 19) and E=50 eV (R=24), where E is the excess energy and R is the ratio of the kinetic energy of the ejected electrons. The changes in the TDCSs with "E" and "R" are presented. The gerade (a(g)) and ungerade (a(u)) dipole amplitudes were determined using four parameters parametrization. The "E" and "R" dependences of the four parameters of a(g) and a(u) arc also presented.

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Angular distributions of photoelectrons from a [Formula presented] shell of fixed-in-space [Formula presented] molecules have been measured for left- and right-elliptically polarized and for linearly polarized light at several photon energies in the region of [Formula presented] shape resonance. That allowed the determination of a set of dipole matrix elements and phase shift differences characterizing the process. These data clearly show the enhancement of the [Formula presented] partial cross section in the resonance simultaneously with an abrupt increase of the corresponding phase shift by [Formula presented], which is the first experimental demonstration of the nature of the [Formula presented] shape resonance in homonuclear diatomic molecules. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevLett.88.063003

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The breakup of D-2 following the absorption of a single photon, leading to four free charged particles interacting via the Coulomb force, has been investigated. Triply differential cross sections (TDCSs) of the two ejected electrons were measured for selected asymmetric kinematic conditions, namely, a 20 eV electron in coincidence with a 5 eV "reference" electron fixed at four different angles. The results are compared with helium TDCSs and, although the respective angular distributions have similar features, there are surprising differences that could have their origin in two-center interference effects.

DOI： 10.1103/PhysRevA.64.062706

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Angular distributions of photoelectrons from both C and O K-shells of the fixed-in-space CO molecule have been measured using the angle-resolved photoeletron-photoion coincidence technique. The measurements have been performed at several photon energies from the ionization thresholds up to about 30 eV above them, where the sigma* shape resonances occur. Experimental results are compared with the multiple-scattering calculations of Diil et al (1976 J. Chem. Phys. 65 3158) and with our new calculations in the relaxed-core Hartree-Fock approximation. Our calculations are in a better agreement with the experimental data though numerical discrepancies remain. The experimental angular distributions are fitted by the expansion in Legendre polynomials containing up to ten terms and the extracted parameters are compared with the corresponding theoretical values.

DOI： 10.1088/0953-4075/33/20/301

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Using the experimental angular distributions of photoelectrons from the K-shells of an oriented CO molecule reported in a companion paper, we have performed a so-called complete experiment and determined 18 dynamical parameters (ten moduli of transition moments and eight phase differences) for the O K-shell, and 16 dynamical parameters (nine moduli of transition moments and seven phase differences) for the C K shell, and compared them with the results of our calculations in the relaxed-core Hartree-Fock (RCHF) approximation. The agreement between theory and experiment is only qualitative, therefore the model has to be improved by including electron correlations. From the analysis of experimental data we proved that the sigma* shape resonance is due to not only the f-wave, as was widely believed earlier, but is due to approximately equal contributions of three partial waves with 1 less than or equal to l less than or equal to 3 for the C R-shell, and four partial waves with 0 less than or equal to l less than or equal to 3 for the O K-shell, with a rather substantial contribution of other partial waves with I less than or equal to 5. From the analysis of the transition moments determined from the experiment it follows that several Cooper minima are likely to exist in partial photoionization cross sections, in particular, in the C 1s sigma --> epsilons sigma and in the O 1s sigma --> epsilond sigma transitions.

DOI： 10.1088/0953-4075/33/20/302

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The angular distribution of photoelectrons from fixed-in-space molecular hydrogen has been measured in the 44-76 eV photon energy range for an ionic state, with a state energy of 38 eV measured from the H-2 ground state, dissociating to H+ + H(n = 2). The photoelectrons are ejected nearly isotropically at 44 eV when their energy is relatively low, while ejection perpendicular to the molecular axis becomes more and more favoured as the photon energy increases. This behaviour is possibly explained in terms of direct photoionization to the 2p pi(u), and 2s sigma(g) states of H-2(+); the former being favoured at 44 eV, and the latter at photon energies far from threshold.

DOI： 10.1088/0953-4075/33/3/320

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Angular correlation patterns of N-5-O23O23 S-1(0) Auger electrons in coincidence with 4d(5/2) photoelectrons in two-step double photoionization of xenon and those of two emitted photoelectrons in coincidence with each other in direct double photoionization of helium have been studied with elliptically polarized photons. Circular dichroism in the angular distribution patterns has been reported in both cases.

DOI： 10.1063/1.1302646

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An essential correlation between intramolecular interference of photoelectron waves and core-hole molecular relaxation is revealed by analyzing the partial wave composition of the calculated angular distribution of photoelectrons in the N and O 1s(-1)sigma(u)* shape resonances of aligned N-2 and CO2. The dominance of coherent (N-2) and incoherent (CO2) interference is revealed, pf and spd hybridization controls the main direction of photoelectron emission from the N and O K shell, respectively. [S0031-9007(98)07498-5].

DOI： 10.1103/PhysRevLett.81.3623

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The design and performance of a 24 m high-resolution spherical grating monochromator (H-SGM) for the undulator beamline (BL-16B) at the Photon Factory are described. With three interchangeable gratings of 400, 900 and 2000 lines mm(-1), the H-SGM is designed to cover the photon energy range 40-600 eV. With a resolving power of approximately 2000 in the photon energy range 40-530 eV, more than 10(11) photons s(-1) have been measured. The best resolutions obtained so far, at a substantially lower photon flux, are greater than 10 000 at 250 eV and 8000 at 400 eV.

DOI： 10.1107/S0909049597019791

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

Angular correlation patterns of N-5-O23O23 S-1(0) Auger electrons in coincidence with 4d(5/2) photoelectrons in the two-step double photoionization of xenon and those of two outgoing 5p photoelectrons in coincidence with each other in the direct double photoionization of xenon were measured with a circularly polarized photon beam from a helical undulator. Circular dichroism was clearly observed in both cases. For the two-step process, the experimental data were in good agreement with the theoretical prediction based on the two-step model.

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The status of cross section measurements carried out with a Mini-EBIS- is reported, here. Single- and multiple-electron transfer processes in collisions of Arq+ (q = 6, 7, 8, 9, and 11) with H-2 and He, and those of C4+ with Ne, Ar and Kr have been investigated at low energies ranging from 0.075 eV/amu to 275 eV/amu and from 0.33 eV/amu to 667 eV/amu, respectively. All data of single-electron transfer cross sections measured for Arq+ -H-2 and -He systems shows a similar tendency to converge toward the Langevin cross section at the low energy end. In the C4+ -Ne system, double-electron transfer is predominant at high energies and it is dominated by the backward scattering at low energies. From the observation of recoil ions produced in C4+ -Ar and -Kr collisions, it is found that the angular distribution of the multiple-electron transfer collisions shifts toward the backward direction in the center-of-mass frame with decreasing collision energy and four-electron transfer processes take place. The importance of the orbiting effect due to the polarization force and the backward scattering are enhanced in the single- and multiple-electron transfer collisions of highly charged ions at low energies.

DOI： 10.1088/0031-8949/1997/T71/026

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Angular distributions of photoelectrons from a 2sigma g shell of fixed-in-space N-2 molecules have been measured for left- and right-elliptically polarized and for linearly polarized light at several photon energies in the region of sigma* shape resonance. That allowed the determination of a set of dipole matrix elements and phase shift differences characterizing the process. These data clearly show the enhancement of the f sigma(u) partial cross section in the resonance simultaneously with an abrupt increase of the corresponding phase shift by pi, which is the first experimental demonstration of the nature of the sigma* shape resonance in homonuclear diatomic molecules.

DOI： 10.1103/PhysRevLett.88.063003

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DOI： 10.11316/butsuri1946.57.408

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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The dynamical information (ten dipole matrix elements and eight phase differences) has been deduced from the measured angular distributions of photoelectrons from O K shell of oriented CO molecules near the ionization threshold in the region of a sigma* shape resonance. Light polarization parallel and perpendicular to the molecular axis has been used. An important contribution of six l sigma partial waves with 0 less than or equal to l less than or equal to 5 to the sigma* shape resonance is demonstrated. A comparison with our calculations in the relaxed core Hartree-Fock approximation reveals only a qualitative agreement, therefore a more advanced theory is needed.

DOI： 10.1103/PhysRevLett.85.46

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：IOP PUBLISHING LTD  

The fully resolved triply differential cross section (TDCS) of helium double photoionization with elliptically polarized light has been determined, both experimentally and theoretically, at the photon energy of 88 eV. The excess energy was shared between the photoelectron pair as 1 + 8, 3 + 6 and 4.5 + 4.5 eV. Simultaneous sign reversal of the Stokes parameters S-1, S-3 resulted in a profound change of shape of the TDCS. This effect can be attributed to the linear dichroism in the case of equal energy sharing, and a combination of the circular and linear dichroisms in the case of unequal energy sharing. Theoretical TDCS was obtained by employing the convergent close-coupling (CCC) method. In contrast to the previous work of Mergel et al (1998 Phys. Rev. Lett. 80 5301) who investigated the circular dichroism at 99 eV photon energy, good agreement is found between experimental and calculated TDCS in all cases.

DOI： 10.1088/0953-4075/32/17/104

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Language：English   Publisher：AMER PHYSICAL SOC  

Energy- and angle-resolved triply differential cross sections have been measured in the double photoionization of helium under equal and unequal energy sharing conditions using right- and left-elliptically polarized photons. Linear dichroism in these cross sections has been observed under the equal energy sharing. For the unequal energy sharing a pure circular polarization effect has been deduced by eliminating the linear polarization contribution.

DOI： 10.1103/PhysRevLett.83.1546

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Language：English   Publisher：KOREAN PHYSICAL SOC  

Angular correlation patterns of N-5-O23O23 S-1(0) Auger electrons in coincidence with 4d(5/2) photoelectrons in the two-step double photoionization of xenon and those of two outgoing 5p photoelectrons in coincidence with each other in the direct double photoionization of xenon were measured with a circularly polarized photon beam from a helical undulator. Circular dichroism was clearly observed in both cases. For the two-step process, the experimental data were in good agreement with the theoretical prediction based on the two-step model.

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The first complete experiment for the C K-shell of CO molecules in the region of the sigma* shape resonance has been performed by detecting photoelectrons in coincidence with fragment ions. Four ratios of dipole matrix elements and four phase shift differences have been extracted from the experi mental data. Their analyses show that, in the sigma* shape resonance due to the l mixing, d and f partial waves give the main contribution to the cross section, and f and g waves give the main contribution to a rapid increase of phase shift by pi.

DOI： 10.1103/PhysRevLett.80.1622

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Angular distributions of 1s sigma(g,u), photoelectrons from CO2 molecules, oriented parallel to the electric vector of incident light, have been measured. The angular distribution patters at sigma(g)* and sigma(u)* shape resonances are significantly different. From those expected in the virtual molecular orbitals concept. The analyses of the patterns have made it clear that the mixing of outgoing photoelectron partial waves and the interference between them are responsible for the observed patterns, unlike N-2 photoionization. Calculations based on a quasiatomic model bare reproduced the observed patterns fairly well.

DOI： 10.1103/PhysRevLett.78.4910

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：IOP PUBLISHING LTD  

The angular correlation between 4d(5/2) photo- and N-5-O23O23 S-1(0) Anger electrons in xenon has been measured for right and left circularly polarized light with 110 eV energy. Thanks to the high degree of circular polarization of the helical undulator radiation, the circular dichroism in the angular correlation has been clearly observed.

DOI： 10.1088/0953-4075/29/9/003

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The cross sections for single-electron capture, including transfer ionization, and for double-electron capture, have been measured for Ar-q+ + HL for q = 6, 7, 8, 9, and 11 with projectile energies from q eV to q keV. Theoretically, the cross sections for Ar6+ and Ar8+ impact were calculated using a molecular-orbital expansion method in the energy region from 240 eV to 80 keV, and are in good agreement with experiment. The single-electron-capture cross sections were found to be more than one order of magnitude larger than those for double capture in both experiment and theory. The single-electron-capture cross sections were also compared to the Langevin cross section, a scaling law developed by Muller and Salzborn [Phys. Lett. 62A, 391 (1977)], and the absorbing sphere model.

DOI： 10.1103/PhysRevA.52.1206

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Charge‐changing cross‐sections σ43, σ42 and σ41 of C4+ injected into CH4, C2H6, C3H8 and n‐C4H10 were measured in the energy range 0.7–400 eV u−1. A tandem mass spectrometer system with an ion source of the EBIS type (Mini‐EBIS) and a collision cell consisting of an octupole ion beam guide was used. It is a significant feature that both the magnitude and energy dependence of the cross‐sections obtained showed very little target dependence for all the hydrocarbon targets studied. Another feature is that σ41 is very close to σ42, and they become flat at low energy, in contrast to the case with an argon target which was studied as a reference. This implies that multi‐electron‐capture processes become dominant in low‐energy collisions with hydrocarbon molecules. Copyright © 1993 John Wiley &amp
Sons Ltd.

DOI： 10.1002/oms.1210280414

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Cross sections for single and multiple electron capture in collisions of C4+ with H-2, N2 and O2 have been measured within the energy range 0.33-666 eV amu-1. Where comparison is possible, the results are in good agreement with previous measurements at higher energies. Below 100 eV amu-1 there are significant differences between experiment and the currently available theories.

DOI： 10.1088/0953-4075/25/13/009

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DOI： 10.1088/0953-4075/25/4/004

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Language：English   Publisher：ELSEVIER SCIENCE BV  

A small size electron beam ion source (mini-EBIS) cooled with liquid nitrogen has been developed for atomic collision research. An experimental technique using mini-EBIS in combination with an octupole ion beam guide (OPIG) has proved very useful for low energy collision experiments including highly charged ions. Single and double electron capture cross sections in collision systems of C4+ -He, N4+ -He and O4+ -He have been measured at low energies from 0.5 to 2000 eV in the center of mass system.

DOI： 10.1016/0168-583X(91)95414-9

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