Atsunari Hiraya

Monochromator for a soft X-ray photochemistry beamline BL27SU of SPring-8

A high-resolution monochromator with varied line space plane gratings (VLSG) and spherical focusing mirrors was installed in one of three branches of BL27SU in SPring-8. The performance of the monochromator was roughly evaluated from the photo ion yield of nitrogen molecule. Furthermore, the kinetic energy of the photoelectron from Xe 5p3/2 orbit was also measured at the same photon energy with the N2 to avoid the influence of natural width. The resolving power over 104 has been confirmed at the N K-edge.

The fluorescence excitation spectrum of aniline in a supersonic free jet: Double minimum potential for the inversion vibration in the excited state

Abstract The fluorescence excitation spectrum of the first singlet transition of aniline in a supersonic free jet has been measured. Vibronic transitions involving the inversion vibration of the NH 2 group in the excited state have been observed. The double minimum potential function in the excited state has been determined from the observed vibrational levels.

Direct absorption spectra of jet-cooled benzene in 130-260 nm

The direct absorption spectrum of benzene in a free jet has been measured in the 130–260 nm region (S1, S2, and S3 states, Rydberg series, and the first ionization limit) using synchrotron radiation as a light source. The absolute molar extinction coefficients (e) of benzene in jets have been determined by scaling measured free‐jet values to the known value in the vapor phase for a broadband at 200.1 nm in the S2 state. The vibrational temperature for ν16 mode was estimated to be 185 K. The maximum value of e of the S1 absorption system was found to be 1400 l mol−1 cm−1 (spectral bandwidth=0.065 nm). A shoulder observed at 205.45 nm in the S2 absorption system is assigned to the S2 origin, induced by pseudo‐Jahn–Teller distortion.

Emission spectra of SiH(A 2Δ→X 2Π) and SiCl2(Ã 1B1→X̃ 1A1) in the VUV photolyses of silane and chlorinated silanes

Vacuum UV photolyses of silane and chlorinated silanes were investigated by using rare gas resonance lamps. Strong emissions, from the A 2Δ→X 2Π transition of SiH and the 1P0→1D2 transition of Si were observed in the photolysis of SiH4 by Ar and Kr resonance lamps. It was suggested that the threshold energies for the appearance of both emissions were lower than the values obtained by the electron impact of SiH4 reported by Perrin et al. A new broad unstructured emission band in the region 300–400 nm was observed in the photolysis of SiH2Cl2 and SiHCl3 by Ar, Kr, and Xe lamps. The band was attributed to the A 1B1→X 1A1 transition of SiCl2 radicals from the measurement of the appearance energy of the emission by using synchrotron orbital radiation.

CCl2(Ã 1B1) radical formation in VUV photolyses of CCl4 and CBrCl3

In vacuum ultraviolet photolyses of CCl4 and CBrCl3 a diffuse emission band was observed in the region of 410–750 nm by Ar i resonance and H Lyman‐α line irradiation. The band was attributed to a CCl2(A 1B1 → X 1A1) transition from the measurements of the appearance energies of the emitters produced from photodissociative excitation of both CCl4 and CBrCl3 using synchrotron radiation. The fluorescence decay of the CCl2(A → X) transition showed a superposition of two lifetime components of 2.17±0.26 and 4.0±0.12 μs at pressures from 10 to 140 mTorr. The pressure dependence of the amplitudes for the two lifetimes suggests the occurrence of collision‐induced intersystem crossing between 1B1 and 3B1 states of CCl2 radicals. The absorption cross section of CBrCl3 was measured for the first time in the 106–200 nm wavelength region and tentative assignments of Rydberg transitions are presented.

Photochemistry of CCl3F and CCl2F2 in the 106–200 nm region

The photoabsorption cross sections and fluorescence excitation spectra of CCl3 F and CCl2 F2 were measured using synchrotron radiation at 106–200 nm. The observed absorption bands were accounted for as Rydberg transitions. The emitters produced from the CCl3 F and CC12F2 photodissociative excitations were attributed to CClF(A 1A‘←X1  A’) and CF2 (A 1B1 →X 1A1 ) transitions, respectively, and their radiative lifetimes were determined to be 626 ± 28 and 58 ± 2 ns. The emission from the CClF(A) starts at 140 nm and increases to 9.1 Mb at 106 nm, and that for CF2 (A) was deduced to be 0.9 Mb at 104.8 nm. The onsets of the fluorescence suggest that the electronically excited CClF and CF2 radicals are formed by the atomic Cl elimination but not by molecular Cl2 releasing process.

New aspects of the ‘‘channel three’’ problem in benzene, as revealed by multiphoton ionization photoelectron spectroscopy

Combining a photoelectron spectroscopic technique with a (1+1) resonant ionization method, we have investigated intramolecular decay processes of benzene in its S1 state under collision‐free conditions. Photoelectron spectra were obtained by selective excitation of benzene with a pulsed UV laser at several single vibronic levels of the S1 state up to an internal energy (ΔE) of 5000 cm−1. These spectra strongly suggest that the excitation of benzene at the vibronic bands above the onset of the ‘‘channel three’’ is followed by intramolecular vibrational redistribution within the S1 state. It is concluded that there are no decay channels faster than this redistribution process up to ΔE=5000 cm−1 at the first decay stage. The results of the integrated multiphoton ionization intensity distribution over the vibronic bands, as well as the internal‐energy dependent spectral changes observed in the photoelectron spectra, also strongly suggest that the channel three is initiated by the redistributed vibrational mod...

Synchrotron radiation-assisted etching of silicon surface

The photo-assisted etching of heavily phosphorous-doped polycrystalline silicon by chlorine was studied using synchrotron radiation as an extreme ultraviolet (EUV) light source. The quantum yield for the removal of the Si atoms at a chlorine pressure of 0.3 Torr was found to be about 0.5% photon-1 using the Ti-filtered light, which is mostly in the EUV region, 1-20 nm. Formation of electronically excited Cl+ ions upon EUV irradiation was confirmed by emission spectroscopy. Negative bias applied to the Si crystal was found to increase the etch rate.

DESIGN OF A FLAT FIELD SPECTROMETER FOR SOFT X-RAY EMISSION SPECTROSCOPY

A spectrometer for soft X-ray emission spectroscopy was designed and constructed. The aims of this spectrometer are high detection efficiency and realizing the energy resolution of 1000 (E/ΔE) in a compact size. To satisfy these requirements, a flat field spectrometer with a varied line spacing grating and a CCD detector was chosen. Furthermore, the configuration without the entrance slit was employed. For compact flat field spectrometers, the spectral dispersion on the detector is sometimes smaller than the spatial resolution of existing detectors restricting maximum energy resolution. The spectral dispersion on the detector was optimized to balance with the spatial resolution of CCD. Optical performance was tested with a ray-tracing program. The spectrometer covers 250–900 eV, with two gratings. Taking into account the spatial resolution of a CCD detector, the maximum energy resolution of the spectrometer is estimated to be about 1000 (E/ΔE) for the beam size of 10 μm. Using the constructed spectrometer, test experiments were performed at the beamline BL27SU in SPring-8.

Photoexcitation of dimethyl sulfide and dimethyl disulfide in the vacuum ultraviolet region: Rydberg states and photofragment emissions

Abstract Photoabsorption cross sections and fluorescence excitation spectra of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) vapors have been studied in the 110–220 nm region using synchrotron radiation. For DMS, a new Rydberg series originating from the ns orbital is identified. A number of broad bands from DMDS are assigned as Rydberg transitions. Emissions from DMS and DMDS are assigned as the CH3( A - X ) band. For DMDS, another emission which is attributable to the S2(B-X) band appears in the excitation below 125 nm. Photodissociation processes forming the excited fragments are discussed.