Toshio Ibuki

Vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8

The vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8 are reported for the wavelength region 107–220 nm using synchrotron radiation as a light source. Absorption maxima of these compounds were found at the exciting wavelengths of 115–119 nm. Broad peaks observed were mostly assigned as primarily Rydberg transitions of the σSiH and σSiSi bonding electrons to the 4s, 4p, and 4d orbitals. The absorption features of germane resemble those of monosilane. In the photoexcitation of monosilane, the emission of the SiH(A 2Δ→X 2Π) transition was observed and its onset was found to be 132±2nm. The absorption spectrum of disilane showed five peaks. They were mostly assigned as 2a1g→4s, 2a1g→np(n=4−6) transitions and the strongest band was overlapped by 1eg→4d and 1eu→4p Rydberg transitions. In trisilane molecules three very weak and broad peaks were recognized and assigned as 3b2→4s, 4p and 4a1→4s, 4d Rydberg transitions. The strongest band was tentatively assigned as the superposition of...

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.

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.

PHOTODISSOCIATION OF HYDROGEN CHLORIDE AND HYDROGEN BROMIDE

The Doppler profiles of the hydrogen atom photofragments from the photodissociation of HCl and HBr at 157 and 243 nm are observed to determine the symmetries of the photoexcited states by using a resonance enhanced multiphoton ionization technique. The phototransitions are perpendicular for HCl at 157 nm and 193 nm and for HBr at 157 nm and 243 nm. Isotope effects on the branching ratios of [Cl*(2P1/2)]/[Cl(2P3/2)] are observed for the photodissociation of HCl and DCl at 157 and 193 nm. Our results indicate that in the photodissociation processes of HCl (A 1Π) the dynamical curve crossings during the breakup of the molecule play important roles in the determination of the branching ratio.

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.

CHARACTERIZATION OF SILICA GLASSES SINTERED UNDER CL2 AMBIENTS

Chlorine incorporated into silica glasses by sintering porous soot rods under Cl2/He atmosphere or by fabricating with plasma methods were found to be mostly as ≡SiCl, which gives rise to an optical absorption tail above ≂7.5 eV. The cross section of the optical absorption at ≂7.77 eV (160 nm) was found to be 1.14×1020 cm2. This value was almost the same as that of ≡SiCl in SiCl4 molecule in the gas phase. A minor fraction (10−3∼10−1) was found to be present as Cl2 molecule, which gives the absorption band at 3.8 eV.

Absorption spectra of SiCl4, Si2Cl6, SiF3CH3 and GeF4 in the VUV region

Abstract In the range 110–200 nm the absorption features of Si2Cl6 closely resemble those of SiCl4 and the peaks observed are tentatively assigned to the Rydberg transitions of a Cl lone-pair electron. Two diffuse bands in the SiF3CH3 absorption are also assigned to Rydberg excitations. The spectrum of GeF4 shows a broad band considered to be a valence excitation of the outermost orbital. The emission of the SiCl2 (A1B1→X1A1) transition was found in the photoexcitation of Si2Cl6.

Dissociative single, double, and triple photoionization of silicon tetrafluoride in the valence shell and silicon 2p regions (hν=33–133 eV)

The photoionization of SiF4 in the valence shell and Si2p innershell regions has been studied using time‐of‐flight mass spectrometry and synchrotron radiation over the photon energy range 33–133 eV. Photoionization branching ratios are reported for stable singly and doubly charged ions arising from the various possible molecular and dissociative photoionization processes. The time‐of‐flight mass spectrometer used in the present work employs very efficient ion extraction fields and this results in very much higher relative abundances of energetic fragmentations than were reported in earlier published work [Lablanquie et al., J. Chem. Phys. 90, 7078 (1989)]. Photoion–photoion coincidence (PIPICO) techniques have been used to investigate the relative yields of Coulomb explosion decomposition products and threshold energies for dissociative double photoionization in the valence shell and silicon 2p regions. The dominant process in the Si2p region is (F++Si+). The PIPICO spectra show additional peaks with thre...

Lifetimes of N2O+(A), CS+2(A), and CS+2(B) states produced by pulsed EUV photons

Pulsed Ne i resonance lines (73.6 and 74.4 nm) were generated by a dc discharge lamp consisting of a charging resistor, a coaxial capacitor, and a spark gap. By a single‐photon counting technique, the radiative lifetimes of N2O+(A 2Σ+, v′1=0 and 1), CS+2(A 2Πu), and CS+2(B 2Σ+u) states were measured. The Stern–Volmer treatments gave the quenching rate constants for the excited ions in the collision with the neutral parent triatomic molecules.