Eiji Shigemasa

High-resolution and symmetry-resolved oxygen K-edge spectra of O2

Abstract High-resolution ion-yield and electron-yield spectra and “symmetry-resolved” ion-yield spectra have been measured at the O K-edge of O 2 . The 1s—π* ( 3 Π) and 1s—σ* ( 3 Σ − ) bound-state resonances are clearly resolved, where the σ* resonance is split into two features. Many Rydberg transitions converging to the 4 Σ − and 2 Σ − ionization thresholds are found on the 1s—σ* resonance, but above the 4 Σ − threshold the Rydberg series converging to the 2 Σ − threshold show only a broad band. They are interpreted with the help of ab initio SCF-CI and frozen-core calculations for the core-excited states with four open shells. The Rydberg series are assigned to the 1s—3sσ, 1s—3pπ, and 1s— n pσ ( n = 3, 4, …) transitions. The splitting of the σ* resonance arises from the exchange interaction; however, in contrast with the Rydberg states, the core-to-valence (1s—σ*) excited state related to the 2 Σ − spin coupling is lower in energy than the 1s—σ* state related to the 4 Σ − one.

Renner–Teller effect and Rydberg‐valence mixing in the N and O K‐edge photoabsorption spectra of N2O

We have measured high‐resolution angle‐resolved ion‐yield spectra of the O and N 1s excited N2O molecules (Nt–Nc–O) and investigated them with the help of ab initio quantum chemical calculations. The peak width of the Nc 1s→π* transition is larger than that of the Nt 1s→π* one. This mainly arises from different populations of bending vibrations excited through the Renner–Teller effect, which breaks the degeneracy of the 1s→π* excited states by bending the linear molecule. The angular distribution of fragment ions emitted after the Auger decay is also affected by the Renner–Teller effect. That is, fragment ions significantly lose the information of the Π symmetry of the linear molecule. For the 1s→Rydberg excitations no Renner–Teller effect is observed and the angular distribution is directly related to the Σ and Π symmetries. Furthermore, it is found that the peak intensities of the O and Nt 1s→nsσ Rydberg transitions are unusually large. The N2O molecule has two σ* orbitals, σs*(8σ) and σp*(9σ), below an...

Compact XFEL and AMO sciences: SACLA and SCSS

The concept, design and performance of Japans compact free-electron laser (FEL) facilities, the SPring-8 Compact SASE Source test accelerator (SCSS) and SPring-8 Angstrom Compact free electron LAser (SACLA), and their applications in mainly atomic, molecular and optical science are reviewed. At SCSS, intense, ultrafast FEL pulses at extreme ultraviolet (EUV) wavelengths have been utilized for investigating various multi-photon processes in atoms, molecules and clusters by means of ion and electron spectroscopy. The quantum optical effect superfluorescence has been observed with EUV excitation. A pump?probe technique combining FEL pulses with near infrared laser pulses has been realized to study the ultrafast dynamics of atoms, molecules and clusters in the sub-picosecond regime. At SACLA, deep inner-shell multi-photon ionization by intense x-ray FEL pulses has been investigated. The development of seeded FEL sources for producing transversely and temporally coherent light, as well as the expected impact on advanced science are discussed.

High‐resolution and symmetry‐resolved N and O K‐edge absorption spectra of NO

High‐resolution electron‐yield and ‘‘symmetry‐resolved’’ ion‐yield spectra have been measured at the N and O K edges of a 2Π open‐shell molecule, NO. Several Rydberg transitions converging to the 3Π and 1Π ionization thresholds are found. The core‐to‐valence and core‐to‐Rydberg transitions are interpreted with the help of ab initio self‐consistent‐field configuration‐interaction and frozen‐core calculations for the core‐excited states with three open shells. It is found that the equivalent‐core model (N*O=O2) breaks down in discussing the state ordering of the three N 1s–2pπ* excited states, 2Δ, 2Σ−, and 2Σ+. It is important to consider explicitly the core hole and the exchange repulsion between the core and π* electrons.High‐resolution electron‐yield and ‘‘symmetry‐resolved’’ ion‐yield spectra have been measured at the N and O K edges of a 2Π open‐shell molecule, NO. Several Rydberg transitions converging to the 3Π and 1Π ionization thresholds are found. The core‐to‐valence and core‐to‐Rydberg transitions are interpreted with the help of ab initio self‐consistent‐field configuration‐interaction and frozen‐core calculations for the core‐excited states with three open shells. It is found that the equivalent‐core model (N*O=O2) breaks down in discussing the state ordering of the three N 1s–2pπ* excited states, 2Δ, 2Σ−, and 2Σ+. It is important to consider explicitly the core hole and the exchange repulsion between the core and π* electrons.

Renner–Teller splitting in the C 1s→π* excited states of CS2, OCS, and CO2

Fragment ions energetically emitted following the perpendicular (ΔΛ=+1) transitions of C 1s→π* of CS2, OCS, and CO2 are observed not only in the perpendicular (90°) direction but also in the parallel (0°) to the linear polarization; that is, ions have a momentum orthogonal to the linear molecule. This arises in the Renner–Teller (RT) vibronic coupling of bending vibrations in the C 1s→ in-plane π* excited state with a bent equilibrium geometry, though the RT splitting between the C 1s→ out-of-plane π* state with a linear geometry and the C 1s→ in-plane π* state is not visible directly due to the lifetime broadening. The 0° ion yield is relatively small in CS2 but is comparable to the 90° yield in CO2; in the latter the peak maximum at 0° is 0.06 eV lower than at 90° and the anisotropy parameter β is heavily dependent on the photon energy. In CO2 a great number of unresolved bending vibrations are coupled. The half-width at half-maximum on the lower energy side of the π* peak is much more sensitive to the ...

Design of a transmission grating spectrometer and an undulator beamline for soft x‐ray emission studies

A soft x‐ray undulator beamline and an x‐ray emission spectrometer have been designed for soft x‐ray emission studies. The beamline has a varied‐line‐spacing plane grating monochromator, which enables the energy resolution over 104 with a beam size down to 10 × 60 μm2. The x‐ray emission spectrometer has a Wolter type I mirror, a free‐standing transmission grating, and a back‐illuminated CCD. A high collection angle up to 1.5 × 10−3 sr is achieved by utilizing the Wolter mirror as a prefocusing system. The CCD is mounted at 1400 mm downstream of the grating on a Rowland torus mount. Diffracted x‐rays are detected in the normal incidence geometry, resulting in high detection efficiency. The energy resolution is limited by the figure errors of the optical elements and the spatial resolution of the detector.

Vibronic coupling and valence mixing in the 1s→Rydberg excited states of C2H2 in comparison with N2 and CO

Abstract Angle-resolved ion-yield spectra are reported for the C1s→Rydberg excitations of linear acetylene C 2 H 2 in comparison with N 2 and CO. The 3σ u * valence state is observed in the 3sσ g Rydberg region with no mixing. The 3pσ u state is found in the same region as the C1sσ g →3pπ u state, which shows only totally symmetric vibrations. This is the first to observe that the Rydberg state in C 2 H 2 keeps gerade and ungerade symmetries without vibronic coupling through antisymmetric stretching vibrations related to core–hole localization. On the other hand, the lowest 1π g * valence state induces vibronic coupling through bending vibrations in the 3σ u * and 3sσ g states.

Application of a simple asynchronous mechanical light chopper to multielectron coincidence spectroscopy

A simple asynchronous mechanical light chopper, based on modification of a turbo-molecular pump, has been developed to extend the interval between light pulses in single bunch operation at the Photon Factory storage ring. A pulse repetition rate of 80 kHz was achieved using a cylinder rotating at 48000 rpm, with 100 slits of 80 microm width. This allows absolute timing of particles up to 12.48 micros instead of the single-bunch period of 624 ns. We have applied the chopper together with a light pulse monitor to measure multielectron coincidence spectra using a magnetic bottle time-of-flight electron spectrometer. With such a system, the electron energies are determined without any ambiguity, the folding of coincidence spectra disappears and the effect of false coincidences is drastically reduced.

Electronic decay processes following the resonance excitation of the B 1s core electron in BF3

Electron spectroscopy has been carried out to investigate spectator and participant resonance Auger decay processes following the B 1s→2a2‘ excitation in gaseous BF3 molecules using monochromatized synchrotron radiation. The resonance‐enhanced satellite bands corresponding to the spectator Auger electron emission form six broad peaks showing good correspondence with the normal Auger bands. Resonance enhancement of the photolines corresponding to the participant Auger electron emission occurs only for the bonding orbitals having B character.

Auger decays of 1s shake-up and shake-off states in N2 molecules

We have studied Auger decays of the 1s shake-up and shake-off states in N2 molecules with a state-of-the-art multi-electron coincidence method. The multi-electron coincidences reveal overall features of the Auger transitions from the individual core-hole states. The decay features of the shake-up states are interpreted by spectator and participant roles of the exited electrons. It is observed that the valence holes formed at the initial shake-off process remain unchanged during the Auger decay from the shake-off states.