Kazumichi Nakagawa

Reconstruction of BL7B for UV, VIS and IR spectroscopy with a 3 m normal-incidence monochromator

The beamline BL7B at the UVSOR facility for solid-state spectroscopy is currently under reconstruction. This reconstruction mainly involves the replacement of the 1 m Seya-Namioka-type monochromator (50-600 nm) with a 3 m NIM (modified version of McPherson model 2253), which covers the 50-1000 nm range with three gratings. The deviation angle of the gratings is 15 degrees. For linear and circular polarization experiments, the beamline optics consist of a two-grazing-incidence (87.5 degrees ) pre-mirror system and a normal-incidence (15 degrees ) post-mirror.

Natural Circular Dichroism Spectra of Alanine and Valine Films in Vacuum Ultraviolet Region

Natural circular dichroism (CD) of alanine (Ala) and valine (Val) films were measured in vacuum ultraviolet region using a polarizing undulator as a circularly polarized light source. Compared with absorption spectra, CD spectra showed clear differences between Ala and Val films. In order to explain these differences, a time-dependent density functional theory was applied to calculated CD spectra. The calculated CD spectra showed good agreement with the experimental CD spectra.

VUV Photoelectric Yield Spectra in Thin Films of KCl, KBr and RbCl at 80 K

Relative photoelectric yield spectra of thin films in KCl, KBr and RbCl are investigated in the photon energy 7 eV–40 eV range at 80 K as well as at room temperature. Several new characteristics of the spectra due to the thin film specimens and due to the lower temperature are observed. It is revealed that the yield spectra dominantly reflect the photo-absorptions modified by the inelastic electron-electron scattering in the valence excitation region and by the Auger process especially in the core excitation region. A large yield peak due to the next deeper core level K + 3 s or Rb + 4 s is newly identified in a photon energy range of 30–40 eV. Interband thresholds of the yield spectra are observed and the electron affinities are derived.

Oxygen K-edge X-ray absorption near edge structures (XANES) of sublimated films of amino acids

Oxygen K-edge X-ray absorption near edge structures (XANES) spectra of amino acids (glycine, L-alpha-alanine, beta-alanine, L-serine, L-asparic acid and L-tyrosine) were measured. Several peaks of XANES spectra were successfully assigned on the basis of DV-Xalpha calculation.

Chiroptical study of α-aliphatic amino acid films in the vacuum ultraviolet region.

A series of natural circular dichroism (CD) and absorption spectra for films of α-aliphatic amino acids--such as alanine, aminobutyric acid, norvaline, norleucine, valine, leucine, and isoleucine--in the vacuum ultraviolet (VUV) region were observed with the absolute values of optical constants at the undulator-based CD beamline TERAS BL5. Preliminary predictions of some CD spectra were also performed, based on quantum-chemical calculations using the crystal structure. Although the absorption spectra show similar features to each other, significant differences between the CD spectra were found, especially in the 7-8 eV region. The CD spectra of aliphatic amino acids with branched alkyl groups in the side-chain--such as valine, leucine, and isoleucine--exhibit strong negative CD peaks in this energy region. In contrast, the corresponding CD peaks were weak or absent in the spectra of amino acids with straight alkyl groups. Our simple calculation, and the absorption spectra of alkanes, suggest that this difference partly originates from the contribution of the alkyl group. Clear discrepancies between the CD spectra of these amino acids in solutions and those in the solid state were also observed; this is probably caused by the different molecular structures in each state. Our results clearly indicated that CD spectra in the VUV region were very sensitive to the conformations of chiral molecules.

Selective adsorption of atomic hydrogen on a h-BN thin film

The adsorption of atomic hydrogen on hexagonal boron nitride (h-BN) is studied using two element-specific spectroscopies, i.e., near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS). B K-edge NEXAFS spectra show a clear change in the energy region of the π* band before and after reaction with atomic deuterium. On the other hand, N K-edge NEXAFS spectra show only a little change. B 1s XPS spectra show a distinct component at the low binding energy side of a main component, while N 1s XPS spectra show peak broadening at the high binding energy side. These experimental results are analyzed by the discrete variational Xα method with a core-hole effect and are explained by a model in which hydrogen atoms are preferentially adsorbed on the B sites of h-BN. Based on the experimental and theoretical results, we propose a site-selective property of BN material on adsorption of atomic hydrogen.

Vacuum ultraviolet circular dichroism spectroscopy using an ac-modulated polarizing undulator

To obtain vacuum ultraviolet (VUV) circular dichroism (CD) measurements, an Onuki-type crossed undulator in an electron storage ring (TERAS) at the National Institute of Advanced Industrial Science and Technology (AIST) was used as a light source and a polarization modulator was used instead of a photoelastic modulator (PEM). Polarization modification through the beam-line optics was theoretically considered and experimentally examined by polarization analysis. The modulation frequency of 2Hz was chosen to optimize the signal-to-noise ratio. On this basis, VUV-CD spectra of alanine films were measured and calibrated. The resulting CD spectra were consistent with other data obtained that was measured by a conventional CD spectropolarimeter (JASCO, J720WI) at a wavelength range of 190–210nm. The spectra of L- and D-alanine films showed an obvious symmetry with respect to the baseline at a wavelength range of 120–210nm. These results proved that the true CD of the samples was measured. The present technique ...

Circular dichroism of amino acid films in UV-VUV region.

Circular dichroism (CD) spectra of sublimated films of alanine and alanine dipeptide were measured in UV-VUV region. When a film has some linear anisotropy, the apparent CD signal is known to be strongly distributed by linear anisotropy. In order to obtain the true CD spectra, we examined this disturbance for L-alanine films. We measured linear dichroism spectra and CD spectra as a function of the sample rotation angle, turning the sample over. On the basis of these measurements, we concluded that the linear anisotropy contribution to CD was sufficiently small for carefully prepared films. In addition, we revealed that it is essential for accurate measurement to prepare thin film of which thickness is smaller than 100 nm for the case of alanine films. CD of amino acid films was compared with that of aqueous solution. Sign of CD signal of solid films was observed to be the same for aspartic acid, but it was reversed from that of aqueous solution for alanine and alanine dipeptide.

Monochromator for circularly polarized synchrotron radiation in the energy range of 5–250 eV

A new spherical grating monochromator with translational and rotational assembly including a normal incidence mount (SGM‐TRAIN) is under construction at BL 5A of the UVSOR Facility, IMS, and its design concept is reported. The following points have been taken into account in the design: (1) Energy range of 5–250 eV, (2) use both of undulator and bending magnet radiation, (3) linear and circular polarizations, (4) spectral purity, (5) resolution, and (6) length of beamline. It should be stressed that the SGM‐TRAIN is useful for experiments where circularly polarized synchrotron radiation is used. Moreover, the SGM‐TRAIN has the advantage that the small emittance of storage ring and the large space for a long beamline are not necessary.

First observation of natural circular dichroism spectra in the extreme ultraviolet region using a polarizing undulator-based optical system and its polarization characteristics.

Natural circular dichroism (CD) spectra in the extreme ultraviolet (EUV) region down to a wavelength of 80 nm have been observed for the first time, using an alanine thin film deposited on sodium salicylate coated glass as a sample. Calibrated EUV-CD spectra of L-alanine exhibited a large negative peak at around 120 nm and a positive CD signal below 90 nm, which were roughly predicted by theoretical calculations. A CD measurement system with an Onuki-type polarizing undulator was used to obtain the EUV-CD spectra. This CD system, the development of which took five years, can be used to observe even weak natural CD spectra. The polarization characteristics of this system were also evaluated in order to calibrate the recorded CD spectra.