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.     

Gravimetric study of high-pressure sorption of gases in polymers

A gravimetric method for determining precisely the solubility of gases in polymers at high pressure is described. The solubilities of N₂ and CO₂ in low-density polyethylene (LDPE); CO₂ in polycarbonate (PC); and N₂, CH₄, C₂H₆, and CO₂ in polysulfone (PSUL) have been measured as a function of pressure up to 50 atm. Most of the measured sorption isotherms agreed closely with published data, but reproducible and time-dependent hysteresis in the sorption of CO₂, C₂H₆, and CH₄ in glassy polymers, PC, and PSUL, was observed in this study for the first time. Like the well known conditioning effect of high-pressure CO₂ on the sorption capacity of glassy polymers, these hysteresis phenomena are believed to be due to the plasticizing effect of sorbed gases. On the basis of the current data, the dual-mode sorption model including the plasticization by sorbed gas is discussed and a primitive equation for the concentration of sorbed gases in a quasiequilibrium state of sorption or desorption is proposed.     

Stereoselective reduction of α-substituted β-keto esters by hydrostannane/organotin triflate

Stereoselective reduction of α-substituted β-keto esters is achieved by the combined use of hydrostannane/organotin triflate. syn-Aldols are obtained with more than 90% selectivities.     

Synthesis and properties of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]tetraphenylene

The X-ray crystal structure and photophysical properties of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]tetraphenylene, which has been synthesized via a Diels-Alder reaction of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene and 6,7-dihydro-6-hydroxy-7,9-dimethyl-8H-cyclopenta[a]acenaphthylene-8-one, are reported.     

Alignment of iodine species in stretched polyacetylene films

The¹²⁹I Mössbauer spectroscopy has been applied to iodine-doped highly conducting polyacetylene. For the unstretched polyacetylene films, the iodine species of I^?, I ₃ ^? and I ₅ ^? are observed. The polyiodides have symmetrical charge population. In addition to these anions, a small amount of iodines is covalently bonding to the carbon atoms, breaking the double bonds of the main chain. For the stretched polyacetylene films, the measurements were done under the condition that the stretch direction was parallel or perpendicular to the direction of incident ψ-rays. The relative change of the intensities of the Mössbauer quadrupole-split lines reveals the alignment of the polyiodine anions in the stretched film.     

Chemical stability and electroconductivity of 7,7,8,8-tetracyanoquinodimethane salts containing polycation polymers

The chemical and electrical stabilities of 7,7,8,8-tetracyanoquinodimethane (TCNQ) salts composed of neutral TCNQ (TCNQ^?), anion radicals of TCNQ(TCNQ^?·), and polycation polymers were studied by measuring their electronic spectra and resistivities (ρ). The results of spectral and chemical analyses confirmed that TCNQ^?· in TCNQ salts was decomposed to α,α-dicyano-p-toluoylcyanide (DTC^?) as the final product by the intermediate formation of TCNQ^? and p-phenylenediamalononitrile (H₂TCNQ) and that H₂O played an important part in the reaction. From these results it was concluded that TCNQ salts are decomposed by two reaction processes: The resistivity of TCNQ salts increases with the decomposition of TCNQ^?·. Studies on electroconductivity of TCNQ salts assume that the change in resistivity arises from the loss of unpaired electrons which become conduction carriers and also from the disintegration of the TCNQ^? and TCNQ^?· complex which forms the conduction path.     

Synthesis of high surface area hydroxyapatite nanoparticles by mixed surfactant-mediated approach

A new surfactant-mediated approach was developed to synthesize hydroxyapatite (HAp) nanoparticles with high surface areas by calcination of their precursors encapsulated with calcium stearate using mixed surfactant-containing reaction mixtures. Acidic aqueous solution of calcium phosphate was mixed with both or either nonaoxyethylene dodecyl ether (C12EO9) and polyoxyethylene(20) sorbitan monostearate (Tween 60) and then was treated with aqueous ammonium at 25 degrees C. The C12EO9-based single surfactant system yielded an aggregate of platy HAp nanoparticles 20-40 nm in size, whereas the Tween 60-based single and mixed systems led to lath-shaped HAp nanoparticles 2-8 nm wide and encapsulated with calcium stearate. On calcination at 500 degrees C, the stearate-encapsulated HAp nanoparticles in the latter two systems were deorganized into high surface area HAp nanoparticles. Particularly, the HAp nanoparticles in the mixed system exhibited a specific surface area as high as 364 m2 g(-1) that is roughly 3 times larger than 160 m2 g(-1) for those in the single system. The significantly high surface area for the former is attributed to much less adhesion of decapsulated HAp nanoparticles, which originated from the particle-separating effect of the C12EO9 molecules adsorbed on the outer surface of the stearate-encapsulated HAp nanoparticles to inhibit their agglomeration or interfacial coordination. The present results demonstrate that the mixed use of two different surfactants as a source of encapsulating and templating agent and a particle-separating agent is specifically effective for the synthesis of high surface area HAp nanoparticles.