Tomonori Ida

Electronic state of small and large cavities for methane hydrate

It is well known that methane hydrate is aggregates of small and large hydrogen bonded water cavities (composed of 12 pentagonal faces of 20 water molecules, and 12 pentagonal and two hexagonal faces of 24 water molecules, respectively) where one methane molecule is encaged. We calculated the methane molecule in vacuum, the small and large cavities by ab initio MO method to clarify the electronic state. The proton of methane in the cavities is shown to form the weak hydrogen bond (O…H—C) between methane and four water molecules, and the H‐bond lengths and energies in the small and large cavities were estimated as (0.293 nm, 6.8 kJ/mol) and (0.309 nm, 5.2 kJ/mol), respectively. The calculated values of symmetric C—H stretching frequencies and 13C‐NMR chemical shieldings of the methane in the two cluster cavities show good agreement with the experimental ones observed by Sum et al. and Ripmeester and coworker, respectively.

Soft X-ray fluorescence measurements of irradiated polymer films

Fluorescent soft X-ray carbon Ka emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with 40 keV nitrogen or argon ions, at fluences ranging from 1 · 10 14 to 1 · 10 16 cm ˇ2 . The PCS films have been irradiated with 5 · 10 15 carbon ions cm ˇ2 of 500 keV and/or annealed at 1000∞C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion fluence above 1 · 10 14 cm ˇ2 which we believe is due to the degradation of the PI into amorphous C:N:O. The width of the forbidden band as determined from the high-energy cut-oA of the C Ka X-ray excitation decreases with the ion fluence. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is close to either to that in diamond-like films or in silicidated graphite, respectively. ” 1998 Elsevier Science B.V. All rights reserved.

Theoretical X-ray photoelectron and emission spectra of Si- and S-containing polymers by density-functional theory calculations using model molecules

Abstract The X-ray photoelectron and emission spectra (XPS and XES) of Si- and S-containing polymers [(–Si{–CH 2 –} 3 ) n (PCS), (–Si(CH 3 )(OH)–O–) n (PMHSO), (–Si(C 6 H 5 )(OH)–O–) n (PTES), (–Si(C 6 H 5 )(OH)–O–Si(CH 3 )(OH)–O–) n (PPMHSO), (–C 6 H 4 –O–C 6 H 4 –SO 2 –) n (PES)] were simulated by the deMon density-functional theory (DFT) calculations using the model molecules. The theoretical valence photoelectron and C Kα X-ray emission spectra showed good accordance with some experimental ones. The combined analysis of the valence XPS and C and O Kα XES enables us to divide the observed valence electronic distribution into the individual contributions for pσ-, pπ- and non-bonding MOs of the polymers.

Structural analysis of AgxCu1−xI (0≤x≤0.5) by solid 63Cu NMR and X-ray diffraction methods

Abstract 63 Cu NMR and X-ray diffraction methods have been used to investigate the temperature dependence of the nuclear chemical shifts and the diffraction patterns, respectively, for mixed crystal Ag x Cu 1− x I (0 x T d CuI 4 3− and O h CuI 6 5− species, as obtained by the finite perturbation theory in an ab initio Gaussian 94 program using double-ζ basis set for Cu and I atoms. In the case of the nonlinear temperature dependence of the shift, we introduce the shift model as proposed by Negita and coworkers: The shift is also due to the cation which moves to the qausi-stable interstitial octahedral sites.

Deuterium NMR study of molecular dynamics and phase transition in acetonitrile crystal.

The molecular dynamics and local structure in the alpha and beta phases of CD(3)CN were studied by (2)H NMR spectroscopy. From the (2)H NMR spin-lattice relaxation time (T(1)), the activation energies of the rotation of the CD(3) group about the C(3) axis in both phases were found to be 6.2 and 11 kJ mol(-1), respectively. These activation energy values suggest that the packing between CD(3)CN molecules in the alpha phase is weaker than that in the beta phase. The slow structural change of the crystal due to the alpha-beta phase transition was investigated using the (2)H NMR spectra and T(1). A jump of CH(3)CN between two neighboring sites in the hydrogen-bond network accompanying the molecular reorientation was observed by the (2)H NMR 2D exchange spectra and the stimulated-echo method in the alpha phase. Vacancy diffusion occurred in the one-dimensional hydrogen-bond network in the alpha phase.

Time-resolved EPR study of radicals from 2,2-dimethoxy-2-phenylacetophenone in ethylene glycol after flash photolysis

Abstract The dynamic behaviour of transient free radicals generated by laser pulse photolysis (with λ =351 nm) of 2,2-dimethoxy-2-phenylacetophenone (DMPA) in ethylene glycol solutions have been studied by time-resolved EPR at room temperature. A main result of the study is a suitable evaluation method for radical systems with CIDEP in the case of very close hyperfine lines and hence with a overlap of several signals. The evaluation of single EPR time-profile signals requires in this case to take in account also the influence of the near resonance positions, what successfully has been done. The formation and decay of the two spin polarized radicals, 7,7-dimethoxy-benzyl (R 1 ) and benzoyl radical (R 2 ), has been observed. For R 1 the relaxation time T 2 was determined with a good accuracy and the rate constants k 1 and k 2 were estimated by fitting the time evolution of the EPR signal at resonance and near resonance positions of the field using the Bloch equations and direct Fourier transform analysis. Radicals from DMPA in the high viscous solvent ethylene glycol have been proved to be an excellent model system for this study however the treatment is applicable also for other systems.

Chemical reactions in polymers induced by ion beam mixing: fluorescence X-ray measurements

Fluorescent soft X-ray emission spectroscopy (XES) is used to study chemical reactions in polyimide (PI), poly- ethersulphone (PES) and polycarbosilane (PCS) films induced by ion-beam mixing. It is found that the fine structure of the 14 22 carbon XES of the PI and PES films is modified after irradiation with fluences above 1310 cm , which is attributed to the degradation of the molecular structure in amorphous C:N:O. The width of the electronic gap decreases with the ion fluence, in correlation with reported increase of conductivity and optical absorption. The bonding configuration of free carbon precipitated in a matrix of a-SiC after irradiation of PCS is closer to that of diamond-like carbon than in a film submitted to combined treatments of irradiation1annealing or direct annealing. Nevertheless clusters formed in the annealed 2 PCS films are less sp -hybridized than in silicidated graphite or sputtered Si:C:H films.

Polymer conversion into amorphous ceramics by ion irradiation

We present results of X-ray fluorescence measurements (carbon Kα and Si L2,3) of methylhydroxylsiloxane and phenylmethylhydroxylsiloxane films. The films are converted into amorphous ceramics by irradiation with 500 keV C and 3 MeV Au ions. Changes in the composition (O/Si ratio) of some polysiloxane films are found when treated with ion irradiation. It is shown that ion irradiation induces a segregation of carbon atoms from methyl groups into diamond-like clusters whereas carbon atoms from phenyl groups maintain their sp2 configuration.

Phase transitions, hydrogen bond and crystal dynamics of p-methylbenzyl alcohol as studied by single crystal X-ray diffraction and 2H NMR

The title compound (pMBA) was found to undergo a first-order phase transition at 211 K (Tc1). Another transition with subtle enthalpy change appeared at 172 K (Tc2). Crystal structure determinations at various temperatures revealed that the transition at Tc1 was accompanied by remarkable changes in the molecular conformations around the CH2-C and O-CH2 bonds and a reversal of the direction of the O-H O hydrogen bond. Experiments of 2H NMR were carried out on pMBA-d where the hydroxyl hydrogen of pMBA was selectively deuterated. Analyses of the 2H NMR spectra and the temperature dependence of T1 of the 2H NMR indicated occurrence of jumping motions of 2H between asymmetric potential wells at temperatures lower than Tc1

The electronic structure of TPD films grown by different methods

Abstract We present X-ray photoelectron spectra and X-ray emission spectra of N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) films excited with synchrotron radiation. The measurements are compared with density-functional theory calculations performed for a TPD monomer and the electronic structure of this material is discussed in detail. The TPD films studied in this work were prepared by ionized and neutral cluster beam deposition (ICBD and NCBD, respectively) as well as by thermal evaporation. X-ray fluorescence measurements show that the ICBD technique provides the most promising way of preparing high quality TPD films with strong electroluminescence. C–N bonds in the TPD structure are destroyed under NCBD as well as under thermal evaporation.