Effects of strain on the dissociation dynamics of O2 on Si(001)

There are two distinctive channels in the dissociation reaction of O2 on Si(001)-(2 x 1): a trapping-mediated channel and a direct-activated channel. Externally applied tensile strain along the <110> direction on the (001) surface is found to suppress the dissociation via a direct-activated channel and to enhance that via a trapping-mediated channel in the temperature range between 200 and 300 K. It has been demonstrated that the dissociation dynamics involving elementary processes such as inelastic scattering and trapping, desorption and/or dissociation from a trapping precursor, and direct dissociation are sensitively influenced by the strain to change the branching ratio of the dissociation reaction.     

Finite element approximation of -surfaces

In this paper a piecewise linear finite element approximation of -surfaces, or surfaces with constant mean curvature, spanned by a given Jordan curve in is considered. It is proved that the finite element -surfaces converge to the exact -surfaces under the condition that the Jordan curve is rectifiable. Several numerical examples are given.

     

Phase structures of the N-acetyl-L-glutamic acid oligomeric benzyl esters (exact residue numbers 4, 6, 8, and 12)–dioxane systems and their optical properties

A series of N-acetyl-L-glutamic acid oligomeric benzyl esters with exact residue numbers (4, 6, 8, 10, and 12) has been synthesized by a stepwise procedure. It has been found that the phase maps of these oligomer-dioxane systems consist of three regions (I : an isotropic solution, II : a liquid crystalline phase, and III : a two-phase (I and II) solution). In particular, for the samples with residue numbers 6, 8, and 12, selective light scattering of coloured regions in the transparent II and III (bottom-layer) regions have been investigated by the use of UV-visible absorption spectra, leading to the conclusion that there exists a helical axis in the structure of the supramolecular aggregates formed by these oligomeric molecules.     

Enhanced electron-capture decay rate of 7Be encapsulated in C60 cages

The decay rate of 7Be electron capture was measured in C60 and Be metal with a reference method. The half-life of 7Be endohedral C60 ((7)Be@C(60)) and 7Be in Be metal (Be metal (7Be)) is found to be 52.68+/-0.05 and 53.12+/-0.05 days, respectively. This amounts to a 0.83% difference in electron-capture decay half-life between (7)Be@C(60) and Be metal (7Be). Our result is a reflection of the different electron wave functions for (7)Be@C(60) inside C60 compared to the situation when 7Be is in a Be metal.     

Stereospecific polymerization of o-methoxystyrene by anionic initiators

o-Methoxystyrene was polymerized with n-butyllithium (n-BuLi), Na naphthalene, and K dispersion as initiators in tetrahydrofuran (THF) and toluene. The stereoregularity of the polymer was investigated by means of the NMR spectroscopy. The methoxy resonance of the spectrum split into ten components due to the tactic pentads. It was found by x-ray examination that the polymer obtained by n-BuLi in toluene at ?45°C was crystalline and highly isotactic. In THF, the stereospecificity of the polymerization was independent of the initiator, and the isotacticity of the polymer increased with increasing reaction temperature. In toluene, the stereospecificity depended on the initiator; i.e., n-BuLi gave a polymer with higher isotacticity than that given by phenylsodium. The fraction of isotactic triad of the polymer obtained by n-BuLi in toluene at ?78°C was more than 90%, but 50% at 50°C. The presence of ca. 1% THF in toluene led to a steep decrease in the isotacticity even at ?78°C. The tacticity of the polymer given by Na naphthalene was not affected by the existence of NaB(C₆H₅)₄ in THF. The polymerization in THF could be explained by Bovey's “single σ” process, while a penultimate effect was observed in the polymerization by n-BuLi in toluene.     

Anionic copolymerization of 1,1-diphenylethylene and 2,3-dimethylbutadiene

1,1-Diphenylethylene (M₂) and 2,3-dimethylbutadiene (M₁) were copolymerized with n-butyllithium in tetrahydrofuran. The rate of consumption of each monomer was followed by the change of high resolution NMR spectra of the reaction mixture. The copolymerization proceeded alternately, if the ratio of initial monomer concentrations, [M₂]₀/[M₁]₀, was sufficiently larger than unity. By assuming the rate constant k₂₂ to be zero, the constants k₂₁ were obtained from the consumption rates of the monomers. In the alternating copolymerization, 2,3-dimethylbutadiene was incorporated into the copolymer only as the 1,4-structure, while the 1,2-structure was predominant in homopolymerization.