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The dissociation and ionization dynamics of CF3I and CH3I molecules were investigated using a pump-and-probe technique that employs a soft x-ray free-electron laser (SACLA) in Japan. First, time-resolved inner-shell photoelectron... more
The dissociation and ionization dynamics of CF3I and CH3I molecules were investigated using a pump-and-probe technique that employs a soft x-ray free-electron laser (SACLA) in Japan. First, time-resolved inner-shell photoelectron spectroscopy was employed to observe the ultrafast reaction of CF3I by monitoring iodine 4d electrons. The change in the I 4d state observed in the photoelectron spectra is found to occur with a rise time τ of approximately 40 fs after a pump laser pulse, which is faster than that observed when an ultrafast gas-phase electron diffraction technique is employed. This implies that the inner-shell photoelectron spectroscopy is more sensitive to the potential surface near the Franck–Condon region. Second, a strong laser intensity at 266 nm, corresponding to a power density of 1.9 × 1014 W cm−2, can easily ionize CH3I molecules via multiphoton ionization processes, and the time dependence of the valence photoelectron spectra clearly shows that at the picosecond timescale, this pump laser pulse causes spectral peaks to shift owing to space-charge effects in response to the large amount of ions generated. Thus, the SACLA can be a useful tool to investigate not only the dynamical process of molecular dissociation but also the ionization process through the shift in the peaks of photoelectron spectra.
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Abstract Storage Ring Free Electron Laser (SRFEL or FEL) has been developed as a powerful light source owing to its high power, high coherence and unique temporal feature. At UVSOR, we have carried out the two-photon double-resonant... more
Abstract Storage Ring Free Electron Laser (SRFEL or FEL) has been developed as a powerful light source owing to its high power, high coherence and unique temporal feature. At UVSOR, we have carried out the two-photon double-resonant excitation on Xe atoms, utilizing a SR pulse as a pump and an FEL pulse as a probe light. In the first experiment, the two-photon double-resonant excitation of the Xe* 5p5nf autoionization states using the combination of FEL around 570 nm and the undulator radiation have been demonstrated. We are also carrying similar experiments in the shorter wavelength region (around 400 nm) of FEL, where higher Rydberg series of the Xe* 5p5nf states via the Xe* 5p55d intermediate state are accessible. PACS codes: 41.60. Cr; 41.60Ap; 33.80. Rv
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Angle-resolved metastable fragments yields spectra have been measured in the N 1s ionization region of the N(2) and C 1s ionization region of CO. These spectra are compared with zero kinetic energy electron and photoelectron spectra. It... more
Angle-resolved metastable fragments yields spectra have been measured in the N 1s ionization region of the N(2) and C 1s ionization region of CO. These spectra are compared with zero kinetic energy electron and photoelectron spectra. It has been shown that an isotropic metastable fragments yields spectra are almost identical with the ZEKE spectrum, whereas metastable fragments yields spectra with the Σ-Σ transition show similarity with photoelectron spectra. This means that these spectra clearly contain information about two shake-up mechanisms: conjugate and direct shake-up processes. All the peaks in the metastable photofragment spectra can be assigned as either satellite states or double/triple excitation states. Thus, it was shown that angle-resolved metastable photofragment spectroscopy could be used to help characterize multi-electron excitation states in general.
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The vacuum ultraviolet (VUV) absorption spectrum of SF5CF3 was measured over the range 106–200 nm. At 121.6 nm, σ(base e) = (7.8 ± 0.6) × 10−18 cm2 molecule−1, in which quoted uncertainty includes two standard deviation from the... more
The vacuum ultraviolet (VUV) absorption spectrum of SF5CF3 was measured over the range 106–200 nm. At 121.6 nm, σ(base e) = (7.8 ± 0.6) × 10−18 cm2 molecule−1, in which quoted uncertainty includes two standard deviation from the least-square fit in the Beer-Lambert plot and our estimate of potential systematic errors associated with measurements of the reactant concentrations. The VUV
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ABSTRACT Based on recent conceptual and technological improvements for soft X-ray monochromators, a varied-line-spacing plane grating monochromator of the Hetrrick type is installed on the bending-magnet beamline BL4B in the UVSOR... more
ABSTRACT Based on recent conceptual and technological improvements for soft X-ray monochromators, a varied-line-spacing plane grating monochromator of the Hetrrick type is installed on the bending-magnet beamline BL4B in the UVSOR facility with a second generation VUV ring of the beam energy of 0.75 GeV. The BL4B has enabled us to realize various spectroscopic investigations under high resolution conditions in the energy range of 90–800 eV. High-resolution angle-resolved photoion-yield spectra (ARPIS) of NO2 and SO2 have been measured in the N and O K-shell excitation regions. The fragment-ion yield spectra measured at 0° and 90° relative to the electric vector of the light reveal excitation symmetries of complicated electronic states. The spectral features are interpreted in comparison with other transition systems, and quantum chemical calculations show strong or weak Rydberg-valence mixing depending on the excitation site in the molecule.
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Abstract. We report here the measurements of vibrationally resolved resonant x-ray emission spectra of core-excited N2 and O2 molecules in the 1s π resonance region. The measured spectra were compared with the simulated spectra calculated... more
Abstract. We report here the measurements of vibrationally resolved resonant x-ray emission spectra of core-excited N2 and O2 molecules in the 1s π resonance region. The measured spectra were compared with the simulated spectra calculated based on the lifetime-vibrational interference theory. We find that the specific excitation to the ν 0 vibrational level in the intermediate core-hole state of N2 molecule leads to clear vibrational structure (ν 0 3) in both of the final electronic X 1Σg (participator band) and a 1Πg (spectator band) states. ...
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DLC films formed by gas cluster ion beam (GCIB) assisted deposition were investigated by NEXAFS using synchrotron radiation
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Linear and reflectron type time-of-flight (TOF) mass spectrometers were used to study chemical reactions of the core-excited large molecules. A linear TOF mass spectrometer was useful for studying an angle-resolved photofragmentation of... more
Linear and reflectron type time-of-flight (TOF) mass spectrometers were used to study chemical reactions of the core-excited large molecules. A linear TOF mass spectrometer was useful for studying an angle-resolved photofragmentation of the core-excited polyatomic molecule. A reflectron type TOF mass spectrometer was powerful to investigate the site-specific photofragmentation. These mass spectrometers were installed as a part of the endstation of the beamline BL8B1 at UVSOR facility of the Institute for Molecular Science, and some features of them are presented in this paper.
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ABSTRACT The three-body dissociation of 1,3,5-triazine (H3C3N3 → 3HCN) has been studied by molecular beam photofragment translational spectroscopy following excitation at 308, 295, 285, 275, 248, and 193 nm. The analysis of the measured... more
ABSTRACT The three-body dissociation of 1,3,5-triazine (H3C3N3 → 3HCN) has been studied by molecular beam photofragment translational spectroscopy following excitation at 308, 295, 285, 275, 248, and 193 nm. The analysis of the measured translational energy distributions of the HCN photofragments has shown that the dissociation mechanism is not, as previously suggested, a symmetric (or synchronous) three-body process but rather is a two-step concerted process, where concerted refers to correlation between the asymptotic velocity vectors of the three ejected HCN fragments. Furthermore, there is evidence that the initially excited electronic state (1E‘‘, 1A2) is deactivated by radiationless processes (internal conversion/intersystem crossing) to a lower electronic and finally dissociative state which is, according to symmetry correlation, the electronic ground state (electronic predissociation).
The emission of low-energy electrons from H2O has been investigated at photon excitation energies in the vicinity of the O 1s ionization threshold. Neutral oxygen Rydberg atoms (O*) were found to form, and the correlation between the... more
The emission of low-energy electrons from H2O has been investigated at photon excitation energies in the vicinity of the O 1s ionization threshold. Neutral oxygen Rydberg atoms (O*) were found to form, and the correlation between the initial inner-shell excited state of H2O and the Rydberg state of O* was determined. The initially excited electron in a Rydberg orbital is shown to remain associated with O* even after the cleavage of two O-H bonds. We also show that the energy discrepancy between two Rydberg states of H2O and O* can be explained by the influence of the post-collision interaction, which becomes stronger as the excitation energy approaches the 1s ionization threshold.
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ABSTRACT A new experimental setup for probing multi-electron processes in molecular inner-shell ionization regions has been developed at the UVSOR facility, IMS. A zero-kinetic-energy electron (ZEKE) analyzer is composed of a lens system... more
ABSTRACT A new experimental setup for probing multi-electron processes in molecular inner-shell ionization regions has been developed at the UVSOR facility, IMS. A zero-kinetic-energy electron (ZEKE) analyzer is composed of a lens system on the basis of the penetrating field technique and an electrostatic analyzer. Two identical ion detectors with regarding grids are utilized for detecting the fragment-ions emitted at 0 and 90 degrees relative to the electric vector of the light, which correspond to the symmetry-resolved photoabsorption spectra. The symmetry-resolved ZEKE spectra have been measured by scanning the photon energy with monitoring the intensity of the coincidence signals between the ZEKE electrons and fragment-ions. The results obtained at SPring-8 using the new setup are reported.
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The high-resolution absolute photoabsorption cross section with an absolute photon energy scale for Ne in the energy region of 864-872 eV (1s-1np Rydberg states) has been measured using a multi-electrode ionization chamber and... more
The high-resolution absolute photoabsorption cross section with an absolute photon energy scale for Ne in the energy region of 864-872 eV (1s-1np Rydberg states) has been measured using a multi-electrode ionization chamber and monochromatized synchrotron radiation. The natural lifetime width of Ne 1s-13p resonance state has been obtained to be 252 +/- 5 meV. The Ne+ (1s-1) ionization potential is determined to be 870.16 +/- 0.04 eV by using the Rydberg formula. These absolute values are supposed to be more reliable than those previously reported.
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ABSTRACT Molecular size effects on the site specific photofragmentation of a core excited molecule were investigated by exciting the N and O K-shells for a series of CH3CO(CH2)nCN (n = 0−3) in which the O and N atoms were separated by... more
ABSTRACT Molecular size effects on the site specific photofragmentation of a core excited molecule were investigated by exciting the N and O K-shells for a series of CH3CO(CH2)nCN (n = 0−3) in which the O and N atoms were separated by successively inserting a CH2 group between the two atoms. The photofragment ions coincident with total photoelectrons were observed by means of a reflectron type time-of-flight mass spectrometer. Little difference was observed in the fragmentation patterns between the N and O K-edges in exciting CH3COCN, CH3COCH2CN, and CH3CO(CH2)2CN. Clear discrimination was observed in the long chained CH3CO(CH2)3CN.
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ABSTRACT Dissociative dynamics of the K shell excited ozone has been investigated by time-of-flight (TOF) mass spectra of fragment ions for the first time. The TOF spectra were acquired at 0 and 90° relative to the electric vector of... more
ABSTRACT Dissociative dynamics of the K shell excited ozone has been investigated by time-of-flight (TOF) mass spectra of fragment ions for the first time. The TOF spectra were acquired at 0 and 90° relative to the electric vector of linearly polarized soft X-ray. In the K shell excitation at the 529 eV photoabsorption peak, the energetic O+ fragment ion was ejected anisotropically, while at the 536 eV band it was isotropic. The β values calculated from simulation of the TOF spectra are consistent with the previous assignments that the 529 eV band is the π* ← OT(1s) resonance excitation and that the 536 eV band mainly consists of two transitions, π*(2b1) ← OC(1s) and σ*(7a1) ← OT(1s) [Gejo et al. Chem. Phys. Lett. 277 (1997) 497]. The TOF spectra show that the π* excitation of terminal oxygen atoms generates more O2+ fragment than the excitation of the center oxygen atom.
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A new experimental setup for probing multielectron processes in molecular inner-shell ionization regions has been developed. Symmetry-resolved zero-kinetic-energy (ZEKE) spectra have been measured by scanning the photon energy along with... more
A new experimental setup for probing multielectron processes in molecular inner-shell ionization regions has been developed. Symmetry-resolved zero-kinetic-energy (ZEKE) spectra have been measured by scanning the photon energy along with monitoring the intensity of the coincidence signals between ZEKE electrons and fragment ions detected at 0° and 90° relative to the electric vector of the light. The actual performance of the method is illustrated by using it to reveal the symmetry decomposition of the multielectron processes, such as double excitations and shake-up satellites, in the K-shell ionization region of nitrogen.
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ABSTRACT High-resolution photoion yield spectra of N2 are measured near the K-shell ionization threshold. Previously unresolved multiple excitations are distinguished in the Σ- and Π-symmetry-resolved spectra, which were obtained from the... more
ABSTRACT High-resolution photoion yield spectra of N2 are measured near the K-shell ionization threshold. Previously unresolved multiple excitations are distinguished in the Σ- and Π-symmetry-resolved spectra, which were obtained from the ion yield spectra recorded at 0° and 90° relative to the polarization direction. The three 1Πu and two 1Σ+u doubly excited states are clearly identified. Furthermore, a weak Π-symmetry feature just at the σ*-shape resonance position (~419 eV) is definitely resolved and assigned to the lowest 1Πu triple excitation with the help of quantum chemical calculations.
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ABSTRACT
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Page 1. Long-lived, highly excited neutral hydrogen atom production following oxygen 1s photoexcitation of gas-phase water molecules This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2011... more
Page 1. Long-lived, highly excited neutral hydrogen atom production following oxygen 1s photoexcitation of gas-phase water molecules This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2011 J. Phys. B: At. Mol. Opt. Phys. ...
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ABSTRACT Angle-resolved metastable fragment yields following photo-excitation have been measured in the photon energy region 405.7-430 eV in N2. Structures corresponding to multiple excitations associated with parallel and perpendicular... more
ABSTRACT Angle-resolved metastable fragment yields following photo-excitation have been measured in the photon energy region 405.7-430 eV in N2. Structures corresponding to multiple excitations associated with parallel and perpendicular transitions are observed in the metastable yield curves recorded using detectors orientated at 0° and 90° to the electric field vector of the linearly polarized incident radiation. The double-excitation structures around 415 eV are interpreted in terms of the overlap of three broad peaks and vibrational progressions. Multiple excitation structures corresponding to high Rydberg states converging to N+2 shake-up satellites are seen above 418 eV. The present work demonstrates that the angle-resolved detection of metastable fragments is an effective spectroscopic tool for probing core-valence multiply excited states in molecules.
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ABSTRACT The novel spectroscopic technique of time-resolved fluorescence–photoion coincidence spectroscopy (TFPICO) has been applied to the investigation of the decay processes of 2p inner-shell excited Ar atoms and clusters. For the Ar... more
ABSTRACT The novel spectroscopic technique of time-resolved fluorescence–photoion coincidence spectroscopy (TFPICO) has been applied to the investigation of the decay processes of 2p inner-shell excited Ar atoms and clusters. For the Ar atom, only that fluorescence accompanying the production of Ar+ showed a strong dependence on excitation energy. This dependence is discussed in terms of competing Auger decay processes. For Ar clusters, the TFPICO spectra for dimer ions (Ar2)+ revealed long-lifetime fluorescence components which can be attributed to the 'third excimer continuum'. With this work we demonstrate the usefulness of this technique for investigating the decay processes of inner-shell excited atoms and clusters.
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X-ray absorption and emission spectra of carbonate ions in aqueous solution were measured at two concentrations. The signals from the ion were extracted via selective excitation and background subtraction. The obtained spectral shape for... more
X-ray absorption and emission spectra of carbonate ions in aqueous solution were measured at two concentrations. The signals from the ion were extracted via selective excitation and background subtraction. The obtained spectral shape for the emission of the ion was well explained by DFT calculations.
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ABSTRACT The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N2 in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy... more
ABSTRACT The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N2 in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy ranges of the incident photons for the target gases were as follows: Ar: 242–252eV (2p Rydberg excitation), Kr: 1650–1770eV (near the 2p ionization thresholds), Xe: 665–720eV (near the 3d ionization thresholds) and 880–1010eV (near the 3p ionization thresholds), N2: 400–425eV (N 1s excitation and ionization). It is the first time to measure the absolute ionization cross sections of Ar, Kr, Xe and N2 over the present energy ranges with the energy resolution of over 10,000. The natural lifetime widths of 2p3/2−14s, 2p3/2−13d, 2p3/2−14d and 2p1/2−14s resonances for Ar, 3d5/2−16p resonance for Xe, and 1s−1πg*(v′=0) resonance for N2 have been obtained based on the cross sections determined. The ionization energies into the Ar+ (2p3/2−1), Ar+ (2p1/2−1) and Xe+ (3d5/2−1) ionic states are also determined using the Rydberg formula.
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The Cl L and C, N, and/or O K edges of the CCl3CN, CF3CN, C6F5CN, 3-CF3C6H4NCO, and CH3OCOCH2CN polyatomic molecules were selectively excited by using synchrotron radiation as a light source. The small CCl3CN and CF3CN molecules did not... more
The Cl L and C, N, and/or O K edges of the CCl3CN, CF3CN, C6F5CN, 3-CF3C6H4NCO, and CH3OCOCH2CN polyatomic molecules were selectively excited by using synchrotron radiation as a light source. The small CCl3CN and CF3CN molecules did not give clear site-specific fragmentation. In the K shell excited aromatics, the phenyl group in the molecules decomposed independently of the initially excited sites. Fragmentation of the CF3 side-chain in 3-CF3C6H4NCO was weak at the terminal O K shell excitation. The aliphatic compound containing both CO and CN groups showed a strong state-specific decomposition at the π*←N(1s) excitation. Reflectron type time-of-flight mass spectrometer with high mass resolution was useful to investigate the reaction processes of the K shell excited polyatomic hydrocarbon molecules.
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Fragmentation of doubly charged ethanol clusters [(C(2)H(5)OH)(n)] following the O 1s ionization has been investigated by means of the photoelectron-photoion-photoion coincidence (PEPIPICO) method. The dominant fission channel of... more
Fragmentation of doubly charged ethanol clusters [(C(2)H(5)OH)(n)] following the O 1s ionization has been investigated by means of the photoelectron-photoion-photoion coincidence (PEPIPICO) method. The dominant fission channel of (C(2)H(5)OH)(n)(2+) was the formation of protonated cluster ion pairs [H(C(2)H(5)OH)(l)(+)/H(C(2)H(5)OH)(m)(+)]. The fragmentation mechanisms of these ion pairs were discussed based on the analysis of the PEPIPICO contour shape. It was clarified that the prominent fragmentation channel was a secondary decay mechanism, where neutral evaporation occurs after charge separation. On the other hand, the formation of small fragment ions was suppressed, excluding the formation of certain specific fragments (H(3)O(+), C(2)H(5)(+)/COH(+), and C(2)H(4)OH(+)). The formation of small fragment ions was suppressed due to the cooling effect caused by the neutral evaporation and the decrease in the electrostatic repulsive force caused by charge separation.
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ABSTRACT The photodissociation of O3 in the Hartley band has been investigated by high-resolution photofragment translational spectroscopy (PTS). At λdiss=248 nm we determined the quantum yield of the dominant decay channel leading to... more
ABSTRACT The photodissociation of O3 in the Hartley band has been investigated by high-resolution photofragment translational spectroscopy (PTS). At λdiss=248 nm we determined the quantum yield of the dominant decay channel leading to O2(1Δg)+O(1D) and the fragment vibrational state distribution. The fragment recoil anisotropy (β=1.25±0.15) was found to be independent of the fragment vibrational states. Between λdiss=275 and 295 nm β assumes a value of 1.6±0.2, which exceeds the value expected for a simple impulsive process. Photofragment yield measurements carried out by PTS between 272 and 286 nm revealed a strong fluctuation of the vibrational state distribution with λdiss. Based on the small but distinct structure superimposed on the broad continuum of the Hartley band and the findings of recent 3D wave packet calculations, we propose this fluctuation, a manifestation of wavelength-dependent partial cross sections, to arise predominantly from an interference effect. The latter occurs between the part of the initially prepared wavepacket which propagates directly into the exit channel and a (minor) part which is temporarily trapped by the motion of the bending and symmetric stretching modes in the excited O3 molecule.
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Hydrogen bonding in acetone clusters was investigated using near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY)... more
Hydrogen bonding in acetone clusters was investigated using near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of the cluster ions were measured as the NEXAFS spectra of acetone clusters. In the carbon K-edge region, the first resonance peak, which was assigned to the C(CO) 1s-->pi( *)(C=O) resonance transition, showed no substantial change in the PIY curves of the acetone clusters, while the C(CH3) 1s-->3ppi(CH(3)) excitation feature was found to be strongly suppressed. The selective suppression of the C(CH3) 1s-->3ppi(CH(3)) resonance transition can be explained by the change in the character of the 3ppi(CH(3)) orbital due to the C=O...H-C type of hydrogen-bonding interaction. On the other hand, the NEXAFS spectra of the acetone molecule and clusters were almost identical in the oxygen K-edge region, except for a small shift in the pi( *)(C=O) resonance of 0.13 eV, because the character of the pi( *)(C=O) orbital remained, regardless of the C=O...H-C hydrogen bonding interaction.