Mitsuhiro Kusaba

Reduction of Sm3+ to Sm2+ by an Intense Femtosecond Laser Pulse in Solution

Samarium 3+ ions in methanol were found to be reduced to the corresponding 2+ ions upon irradiation with intense femtosecond laser pulses. The reduction was observed at both pulses with central wavelengths of 403 nm converted from an 800 fs fundamental pulse and 800 nm with a duration of 43 fs. When the laser wavelength was tuned to the 4f-4f absorption at 403 nm corresponding to the (6)P(3/2) <-- (6)H(5/2) transition, the reduction occurred by multiphoton absorption, presumably due to reaching the deep charge transfer state. In the case of excitation by 800 nm pulses of the fundamental wavelength of the Ti:sapphire laser, the reduction is considered to occur via solvent ionization followed by electron capture by Sm(3+). The product Sm(2+) was detected by its fluorescence, which was observed for the first time in solution and showed a broad spectrum peak around 750 nm with a quantum yield of 0.050 in methanol in the presence of 15-crown-5-ether.

One-photon reduction of Sm3+ to Sm2+

Abstract The photoreduction mechanism of Sm3+ to Sm2+ was studied using a KrF excimer laser. Reduction occurred via a one-photon process (different from previous suggestions). The reduction yield was 0.34 ± 0.09 in a methanol solution of 18-crown-6 with Sm3+. The oxidized solvent (*CH2OH radical) was observed in the transient spectrum.

Synthesis of 2,′:5′,2″-terpyridine and 2,2′:5′,2″:5″,2‴-quaterpyridine and their photocatalysis of the reduction of water

2,2′:5′,2″-Terpyridine (OPy-3) and 2,2′:5′,2″:5″,2‴-quaterpyridine (OPy-4) are prepared by Ni°complex-catalysed polycondensation of 2,5-dichloropyridine in the presence of an excess of 2chloropyridine. These two compounds show more efficient photocatalysis of H2 evolution by the reduction of water than p-terphenyl and p-quaterphenyl in the presence of triethylamine as an electron donor, and RuCl3 or K2PtCl6 as a source of Ruo or Pto colloids which function as an electron mediator. The primary photochemical processes of OPy-n(n= 3 or 4) and the successive reactions have been investigated by γ-radiolysis, pulse radiolysis and laser flash photolysis. The OPy-n molecules are converted to their anion radicals through reductive quenching of the excited states. A mechanism for the photocatalysis of hydrogen evolution is proposed in which the anion radicals supply electrons to protons on the metal colloids. The anion radicals undergo protonation in competition with electron transfer, resulting in the loss of photocatalytic activity.

Mechanistic studies of the one-electron oxidation of water to hydroxyl radicals photosensitized by perfluorinated p-terphenyl

Photo-oxidation of water in a system consisting of perfluorinated p-terphenyl (F-OPP-3) as a photosensitizer, O2 as an oxidative quencher and benzene as a hydroxyl radical scavenger is mechanistically studied by laser flash photolysis and γ-ray and pulse radiolysis. The radical cation of F-OPP-3 (F-OPP-3˙+) is formed via the oxidative quenching of its excited singlet state by O2. The decay of F-OPP-3˙+ observed in transient spectroscopy is enhanced by the addition of water to the system, indicating that F-OPP-3˙+ plays a crucial role in the one-electron oxidation of water.

Visible light induced photo-oxidation of water. Formation of intermediary hydroxyl radicals through the photoexcited triplet state of perfluorophenazine

1,2,3,4,5,6,7,8-Octafluorophenazine (F-Phen) has an absorption spectrum in the longer wavelength extending to the visible-light region and has a more positive oxidation potential than for unfluorinated phenazine. F-Phen has been photolysed with water in acetonitrile under visible-light irradiation to produce stoichiometrically 1,3,4,5,6,7,8-heptafluoro-2-hydroxyphenazine (F-Phen-2-OH). Photolysis of F-Phen with water in the presence of benzene leads to the formation of phenol followed by the disappearance of F-Phen. EPR analysis and laser flash photolysis reveal that the photoexcited triplet state of F-Phen participates in water oxidation to hydroxyl radicals with concurrent conversion to F-Phen-2-OH. The mechanism is discussed with the results of semi-empirical molecular orbital calculations.

REACTION DYNAMICS OF HOT NAPHTHALENE MOLECULES IN THE GAS PHASE WITH ARF LASER EXCITATION

Abstract Laser flash photolysis has been carried out to elucidate relaxation dynamics of highly excited naphthalene in the gas phase. Highly vibrationally excited ‘hot’ naphthalene in the ground state was formed through rapid internal conversion after 193 nm laser excitation. Hot naphthalene was effectively deactivated by nitrogen molecules, and the energy transferred per collision was similar to that of azulene or hexafluorobenzene. The molecule was found to absorb a second photon under high photon density conditions to undergo an intramolecular chemical reaction.

Magnetic field analysis of a hybrid helical microwiggler

Abstract A hybrid helical microwiggler has been designed analyzing its magnetic field by a computational code. It consists of fan-shaped permanent magnets and ferromagnets which are constructed in four layers each period. It is so small that the outer diameter is about 4 cm and periodical length 1 cm. The magnetic field is 3.73 kG for the gap spacing of 5 mm.

Development of a hybrid helical microwiggler with four poles per period

A compact strong test hybrid helical microwiggler has been designed and developed with ten periods, each with length 10 mm and four poles, and gap diameter of 5 mm. One period is constructed with four segments. Each segment has a thickness of 2.5 mm and consists of pentagonal permanent magnets and permendur poles. Each segment is stacked along the wiggler axis and is rotated by an angle of 90/spl deg/ to the adjacent segment. The outer width is only 72 mm. The wiggler is divided into two sections where two kinds of permanent magnet - one with apex angle of 90/spl deg/ and one with 120/spl deg/ - were installed in order to find out the effect of geometrical size for the field. Peak fields of 0.360 and 0.381 T were achieved with small rms variations of about 1.1% and 0.6%, respectively, depending on the geometrical size of the permanent magnet.

Design of a compact Cherenkov Free-Electron Laser

Design of a Cherenkov free-electron laser operating in millimeter wave range was carried out as a test bench for a compact terahertz radiation source. A CW output of 1.8 W is expected at the frequency of 46.4 GHz with 50 keV electron beam. The experimental apparatus consists of Spindt-cathode, double-silicon-slab resonator and super-conducting coil.

Suppression of ablation by double-pulse femtosecond laser irradiation

We have demonstrated the suppression of ablation rate on a silicon surface irradiated by a double-pulse beam with two color laser in time delays of Δt = -900 - 900 ps. The double pulse beam consists of 810nm with 40fs pulse and 405nm with > 40fs pulse. The fundamental-pulse fluence F810 is kept below ablation threshold (Fth, 810nm = 0.190 J/cm2 ) while the second harmonic pulse fluence F405 are kept above the ablation threshold (Fth, 405nm = 0.050 J/cm2 ). We find that ablation rate of silicon is drastically decreased at delay times of 600ps.