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A Hiraya

Publications and source records attributed to A Hiraya.

8 recordsLinked to original sources
PubMed2005

Production of methyl-oxonium ion and its complexes in the core-excited (HC(O)OCH3)n clusters: H/H+ transfer from the alpha carbonyl.

Dissociation of free methyl-formate (MF), HC(O)OCH3, and its clusters (MF)n, (HC(O)OCH3)n, induced by core-level excitation was studied near the oxygen K edge by time-of-flight fragment-mass spectroscopy. Besides the protonated clusters, (MF)nH+ with n < or = 15, we identified the production for another series of (MF)mCH3OH2+ with m < or = 14 as well as methyl-oxonium ion, CH3OH2+, characteristic of hydrogen transfer reactions in the cationic clusters. Here; specifically labeled methyl-formate-d (MFD), DC(O)OCH3 was also used to examine the core-excited dissociation mechanisms. Deuterium-labeled experiments indicated that MFD+ with low internal energies, partially generated after the core excitation, produces CH3OD+ via a site-specific deuterium transfer from the alpha carbonyl in the molecular cation and that CH3OD2+ can be formed via the successive transfer of another deuterium from the neighbor molecule in the clusters. The deuteron (proton) transfer was also found to take place preferentially from the alpha carbonyl of the neighbor molecule for the production of deuteronated (MFD)nD+, (protonated (MF)nH+), clusters. The minimal energy requirement paths were examined for dimer (MF)2+ cation to support the present dissociation mechanisms of core-excited (MF)n clusters using ab initio molecular-orbital calculations.

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PubMed2005

Angular distribution of different vibrational components of the X and B states reached after resonant Auger decay of core-excited H2O: experiment and theory.

Vibrationally resolved spectra have been obtained for the lowest-lying cationic states X (2)B(1), A (2)A(1), and B (2)B(2) of the water molecule reached after participator resonant Auger decay of core-excited states. The angular distribution has been measured of the first four vibrational components of the X state in the photon energy regions including the O 1s-->4a(1) and the O 1s-->2b(2) core excitations, and for different portions of the vibrational envelope of the B state in the photon energy region including the O 1s-->2b(2) core excitation. For the X state, a large relative spread in beta values of the different vibrational components is observed across both resonances. For the B state, a very different trend is observed for the high binding energy side and the low binding energy side of the related spectral feature as a function of photon energy. A theoretical method based on the scattering K matrix has been used to calculate both the photoabsorption spectrum and the beta values, by taking both interference between direct and resonant photoemission and vibrational/lifetime interference into account. The numerical results show qualitative agreement with the trends detected in the experimental values and explain the conspicuous variations of the beta values primarily in terms of coupling between direct and resonant photoemission by interaction terms of different sign for different final vibrational states.

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PubMed1998

Laser-induced fluorescence excitation spectroscopy of N(2)(+) produced by VUV photoionization of N(2) and N(2)O.

Synchrotron radiation emitted from the UVSOR storage ring is monochromated by a grazing-incidence monochromator and introduced coaxially with the second harmonic of a mode-locked Ti:sapphire laser. Sample gases, N(2) and N(2)O, are photoionized into vibronically ground N(2)(+) with the fundamental light of the undulator radiation at 18.0 and 18.6 eV, respectively. Laser-induced fluorescence (LIF) excitation spectra of N(2)(+) from N(2) and N(2)O are measured in the laser wavelength region of the (B (2)Sigma(u)(+), v' = 0) <-- (X (2)Sigma(g)(+), v" = 0) transition at 389-392 nm. The LIF excitation spectra of N(2)(+) exhibit two maxima due to the P and R branches in which rotational bands are heavily overlapped. The rotational temperature is determined by simulating an LIF excitation spectrum by using the theoretical intensity distribution of rotation bands convoluted with the spectral width of the laser.

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PubMed1998

Soft X-ray photochemistry beamline at SPring-8.

Design and construction of a soft X-ray beamline at SPring-8 is reported. The beamline utilizes high-quality linearly polarized soft X-rays obtainable from a figure-8 undulator for the study of photophysical and photochemical processes of atoms, molecules and surfaces in the inner-shell excitation region. It consists of two experimental stations, a photochemistry station and a chemical vapour deposition (CVD) station. A high-resolution grating monochromator is installed at the photochemistry station, while the intense undispersed undulator radiation is used at the CVD station. Unique features of the experimental chambers and of the analysis and characterization systems are described along with those of the monochromator.

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PubMed1998

Undulators at HiSOR - a compact racetrack-type ring.

A compact racetrack-type 700 MeV storage ring (HiSOR) has been constructed at Hiroshima Synchrotron Radiation Center (HSRC). As the ring was planned for synchrotron radiation research on science and technology using VUV to X-rays up to 5 keV with limited size and cost, the ring was designed (i) to realize a high magnetic field (2.7 T) using conventional dipole magnets for higher critical energy, and (ii) to include two straight sections for insertion devices. A linear undulator (25-300 eV) and a new-type helical/linear undulator were installed at the two straight sections. The latter undulator consists of upper and lower jaws, as in a planar undulator; each jaw consists of one fixed magnet array at the centre and two magnet arrays on both sides. By longitudinal displacement of the side magnet arrays, the phase between the vertical and horizontal magnetic fields, and therefore the polarization (right- or left-circular, elliptical, linear) can be selected. The helical/linear undulator gives almost perfect circular polarization at 4-40 eV in the helical configuration without changing the phase of the magnet arrays, as well as linearly polarized light at 3-300 eV in the linear configuration.

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PubMed1997

Development of a tunable UV laser system synchronizing precisely with synchrotron radiation pulses from UVSOR.

A mode-locked Ti:sapphire laser is made to oscillate at the frequency of the UVSOR storage ring, 90.115 MHz, in a multi-bunch operation mode. The third harmonic of the laser is available in the wavelength range 243-280 nm. Synchrotron radiation from an undulator is monochromated by a grazing-incidence monochromator and introduced coaxially with the laser. The temporal profile of the photon pulses is monitored in situ by a luminescing substance/photomultiplier combination. The delay timing between the laser and synchrotron radiation can be changed from 0 to 11 ns by adjusting an electronic module that provides phase-locked loop stabilization of the laser pulse. The reliability and feasibility of this laser-synchrotron radiation combination technique are demonstrated by applying pump-probe experiments to two physical systems. The first system is photodissociation of iodomethane (CHA) with a laser photon, followed by photoionization of I and CH3 fragments with synchrotron radiation. The second, two-photon ionization of He atoms, is studied as the prototype of a time-resolved experiment. The He+ signal counts as a function of the laser-synchrotron radiation delay are found to be enhanced in a narrow time window, which can be interpreted in terms of a short lifetime of the resonant state, He*(1s2p 1P), produced by primary synchrotron radiation excitation.

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