Molecular structures,electronic spectra,and aromaticity of 1,6- and 1,8-dioxa analogues of pyrene and benzo[a]pyrene. Semiempirical molecular orbital calculations

The molecular structures of [1]benzopyrano[6,5,4-def][1]benzopyran, [2]benzopyrano[7,8,1,def]-1-benzopyran, 1-benzopyrano[6,5,4-mna]xanthene, and 2-benzopyrano[7,8,1-mna]xanthene have been optimized by using the PM3 semiemperical MO method. These calculated molecules have been shown to be planar. Their aromaticity has been investigated by use of the HOMA index. The molecules are found to be less aromatic than the correspolding parednt hydrocarbons, pyrene and benzo[a]pyrene. The CNDO/S MO method has been used to interpret th experimental uv-vis specrtoscopic data. The result of the PM3, CNDO/S and HOMA-index clculations are in good arteement with the experimental data.     

Gas permeation of fullerene‐dispersed poly(1‐trimethylsilyl‐1‐propyne) membranes

Homogeneously fullerene‐dispersed membranes were prepared under the conditions in which a 10 wt % poly(1‐trimethylsilyl‐1‐propyne) solution containing 0.5 wt % fullerene was dried under a reduced pressure of 50 cmHg at 100 °C. UV‐vis spectra and microscopic observations of the fullerene membranes indicated that the fullerene was homogeneously dispersed in the membranes. The permeability coefficients of 1‐butene were found to be higher than those of n‐butane in the fullerene membranes, although the permeability coefficients of olefin gases were nearly equal to those of paraffin gases having the same number of carbon in poly(1‐trimethylsilyl‐1‐propyne) membranes containing no fullerene. Pressure dependence of permeability coefficients was clearly observed for the permeation of carbon dioxide, ethylene, ethane, 1‐butene, and n‐butane through the fullerene membranes, while no significant dependence was found for poly(1‐trimethylsilyl‐1‐propyne) membranes except for the permeation of 1‐butene and n‐butane. The pressure dependence of the permeability was explained by the dual‐mode sorption model. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1749–1755, 2000     

Photopolymerization mechanisms of acrylates in poly(methyl methacrylate) films

Photoinitiation processes for photopolymer coating layers have been investigated with respect to quenching rates by a laser flash photolysis using a total reflection cell, as well as to the decomposition‐quantum yield of a sensitizer dye and a radical‐generating reagent by a gel permeative chromatographic analysis (GPC); the sensitizer dye,2‐[p‐(diethylamino)styryl]naphtho[1,2‐d]‐thiazole (DNT) and the radical‐generating reagent, 2,2′‐bis(2‐chlorophenyl)‐4,4′,5,5′‐tetraphenyl‐1,1′‐bi‐1H‐imidazole (BI). From experiments using flash photolysis, strong fluorescence was observed at excitation of 355 nm laser pulse, though no transient absorption was observed. The fluorescence was statically quenched by BI with a quenching distance, R = 11 Å. From the experiments using GPC, the high‐quantum yield of decomposition (Φ) was obtained as Φ (DNT) = 3 and Φ (BI) = 9 for DNT and BI in the presence of acrylate monomers, trimethyrolpropanetri‐acrylate (TMPTA), at 488 nm exposure of 3.36 mJ cm which was required to form a photo‐hardened image, however no decomposition of DNT and BI was detected in the absence of TMPTA. The results imply that the photoinitiator system undergoes efficient static‐dye sensitization and efficient polymerization of the acrylate monomers accompanied with the chain decomposition of DNT and BI. Copyright © 1999 John Wiley & Sons, Ltd.     

Surface reconstruction of clean bcc-Fe{1 1 0}: A quasi-hexagonal top-layer with periodic height modulation

Hexagonal-pillar shaped pure Fe single crystal whiskers with six {1 1 0} side planes were obtained by means of chemical vapor deposition. Atomically resolved scanning tunneling microscopy images obtained on the {1 1 0} surface showed a quasi-hexagonal atomic array with mesoscopic-range periodic height modulation of about 1/3 of an atomic step. This height modulation was found to be a result of an interference between the quasi-hexagonal top-layer and the sub-surface bcc-Fe{1 1 0} layer. Unit vectors of the mesoscopic-range modulation turned out to be expressed as , where and are the primitive vectors of the two-dimensional atomic array in the top-layer and those in the sub-surface layer, respectively. The two-dimensional density of atoms in the top-layer is slightly higher by 0.46% than that in the sub-surface layer.     

Ru(PPh3)(OH)-salen complex: a designer catalyst for chemoselective aerobic oxidation of primary alcohols

Based on the analysis of the mechanism of aerobic oxidation of alcohols using Ru(NO)-salen catalyst, we designed a new complex, Ru(PPh₃)(OH)-salen 3, which was proved to be an excellent catalyst for chemoselective aerobic oxidation of primary alcohols to the aldehydes in the presence of secondary alcohols under ambient and non-irradiated conditions. Complex 3 was also successfully applied to the oxidation of 1-phenyl-1,n-diols to the lactols or the n-hydroxy aldehyde. It is of note that selective oxidation of primary alcohols was achieved even in the presence of activated secondary alcohols.     

Kinetics of the dehydrochlorination of poly(vinyl chloride) in the presence of NaOH and various diols as solvents

The dehydrochlorination of PVC in the presence of NaOH was investigated in different diols. Diethylene glycol (DEG), triethylene glycol (TEG), and propylene glycol (PG) were found to be effective in accelerating the dechlorination of PVC. The dehydrochlorination was promoted in the order TEG > DEG > PG, which was in agreement with the compatibility between PET and the diol. Compatibility resulted in an improved penetration of the PVC particle by the solvent, leading to the acceleration of the dehydrochlorination. The dehydrochlorination of PVC in NaOH/diol followed first-order kinetics, confirming the progress of the reaction under chemical reaction control. The apparent activation energies were 82 kJ mol⁻¹, 109 kJ mol⁻¹, and 151 kJ mol⁻¹ for TEG, DEG, and PG, respectively. The lower the activation energy became the faster the dehydrochlorination of PVC proceeded.     

Rapid discharge-pumped wide aperture X-ray preionized KrF laser

A wide aperture X-ray preionized discharge-pumped KrF excimer laser has been constructed. A flat plate pulse-forming line (36 nF, 340 kV) charges a peaking capacitor (6 nF) through a rail-gap to facilitate a rapid discharge in the laser head. Collimated X-ray preionization is employed to obtain a wide and uniform discharge. The laser is intended to be used as a short pulse amplifier and results are presented when characterized as an oscillator. The active cross-section of the laser beam is 10×8 cm² with 50 cm effective electrode length. The laser pulse energy exceeds 4.7 J in a 28 ns pulse (FWHM).     

Frequency dependence of electron spin-lattice relaxation rate at 5–450 MHz in pristine trans-polyacetylene --- new evidence of one dimensional diffusive motion of electron spin (neutral soliton) ---

Electron spin-lattice relaxation rate T_l^?1 has been measured at low frequencies 5–450 MHz in pristine trans-polyacetylene. Frequency dependence of T_l^?1 gave dimensionality of diffusive motion of electron spins (neutral soliton). Relaxation mechanism was identified as dipolar and hyperfine origin based on an electron spin concentration dependence of T_l^?1.     

Millimeter-wave spectroscopy of the internal rotation hot band (j=2-1) of the Ar-HCN complex

Millimeter-wave absorption spectroscopy combined with a pulsed jet expansion technique was applied to measure the internal rotation j=2-1 hot band of the Ar-HCN complex in the frequency region of 147-287 GHz. In total 153 rovibrational lines, split into hyperfine components due to the nitrogen nucleus, were assigned to the Σ₂-Σ₁, Σ₂-Π₁, Π₂-Σ₁, Π₂-Π₁, Δ₂-Σ₁, and Δ₂-Π₁ subbands. A set of molecular constants for the Σ₂, Π₂, and Δ₂ internal rotation substates, including subband origins, rotational constants, nuclear quadrupole coupling constants, and Coriolis interaction constants, was determined. The internal rotation energy for the Σ₂ state, 412.8949 GHz, is higher than those for the Π₂ and Δ₂ states, 392.3974 and 355.9570 GHz, by 20.498 and 56.938 GHz, respectively, in contrast to the Σ₁ state located by 17.094 GHz lower than the Π₁ state, the anisotropy of potential energy surface affecting the j=2 and j=1 states differently. The rotational and quadrupole coupling constants in the j=2 excited state are quite different from those in the ground state, indicating drastic change in the average structure in the j=2 state from the ground state. The determined molecular constants were compared with those calculated from the potential energy surface computed at the CCSD(T) level.