Flux peaking of channeled ions in interstitial compounds NbO and ZrO13

A double flux peaking has been observed in a planar channeling of a NbO single crystal, while a single peak has been seen on a $\text{ZrO}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ crystal. The experimental results are compared with an analytical calculation based on the continuum model.     

Stabilizing effect of intramolecular lewis base toward racemization of optically active selenoxides

2‐(Methylchalcogenomethyl)diphenyl selenoxides 1 and 2‐{2′‐(N,N‐dimethylamino)ethyl}phenyl alkyl (or aryl) selenoxides 2 , which were expected to be stabilized toward racemization by intramolecular coordination, were synthesized and optically resolved into their enantiomers on an optically active column using high‐performance liquid chromatography. Relationship between the absolute configurations and the chiroptical properties of the enantiomers was clarified by comparing with those of sulfur analogues. Stabilities toward racemization of optically active selenoxides 1a and 1b were nearly equal to that of 2‐{(N,N‐dimethylamino)methyl}diphenyl selenoxide and mesityl phenyl selenoxide. The rates of racemization for optically active selenoxides 2 were found to be faster than that of 2‐{(N,N‐dimethylamino)methyl}phenyl alkyl (or aryl) selenoxides. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:301–311, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20299     

Effects of stacking fault energy on defect formation process in face-centered cubic metals

To elucidate the effect of stacking fault energies (SFEs) on defect formation by the collision cascade process for face-centred cubic metals, we used six sets of interatomic potentials with different SFEs while keeping the other properties almost identical. Molecular dynamic simulations of the collision cascade were carried out using these potentials with primary knock-on atom energies (E_PKA) of 10 and 20 keV at 100 K. Neither the number of residual defects nor the size distributions for both self-interstitial atom (SIA) type and vacancy type clusters were affected by the difference in the SFE. In the case of E_PKA = 20 keV, the ratio of glissile SIA clusters increased as the SFE decreased, which was not expected by a prediction based on the classical dislocation theory. The trend did not change after annealing at 1100 K for 100 ps. For vacancy clusters, few stacking fault tetrahedrons (SFTs) formed before the annealing. However, lower SFEs tended to increase the SFT fraction after the annealing, where large vacancy clusters formed at considerable densities. The findings of this study can be used to characterise the defect formation process in low SFE metals such as austenitic stainless steels.     

Enhancement of ammonia dehydrogenation by introduction of oxygen onto cobalt and iron cluster cations

Reactions of oxygen-chemisorbed cobalt and iron cluster cations (Co(n)O(m)(+) and Fe(n)O(m)(+); n = 3-6, m = 1-3) with an NH(3) molecule have been investigated in comparison with their bare metal cluster cations at a collision energy of 0.2 eV by use of a guided ion beam tandem mass spectrometer. We have observed three kinds of reaction products, which come from NH(3) chemisorption with and without release of a metal atom from the cluster and dehydrogenation of the chemisorbed NH(3). Reaction cross sections and branching fractions are strongly influenced by the number of oxygen atoms introduced onto the metal clusters. Oxygen-chemisorbed metal clusters with particular compositions such as Co(4)O(+), Co(5)O(2)(+), and Fe(5)O(2)(+) are extremely reactive for NH(3) dehydrogenation, whereas Co(4)O(2)(+) and Fe(4)O(2)(+) exhibit high reactivity for NH(3) chemisorption with metal release. The enhancement of dehydrogenation for specific compositions can be interpreted in terms of competition between O-H and neighboring Co-H (or Fe-H) formation.     

Infrared spectra of the CF3I dimer: a concurrent application of matrix-isolation spectroscopy and cavity ring-down spectroscopy

We have observed infrared spectra of the CF(3)I dimer produced in a supersonic jet by matrix-isolation Fourier transform infrared spectroscopy and infrared cavity ring-down (IR-CRD) spectroscopy. In the matrix-isolation experiments, the dimer was isolated in an Ar matrix by the pulse-deposition method. The recorded spectral range covers the symmetric (nu(1)) and doubly degenerate (nu(4)) C-F stretching regions. From the concentration dependence of the matrix-isolation spectra we have assigned one dimer band for each fundamental region. It was not easy to identify the dimer band for the nu(4) band because of the multiplet feature of the monomeric nu(4) band caused by the site symmetry breaking. The spectra of (CF(3)I)(2) in the nu(4) band region were thus also measured in the gas phase by IR-CRD spectroscopy, where we detected two dimer bands. Comparing the observed band positions with the results of quantum chemical calculations, we have assigned the observed dimer bands to the head-to-head isomer. The structure of (CF(3)I)(2) and its photochemical implications are discussed, in comparison with methyl iodide dimer reported previously [Ito et al., Chem. Phys. Lett. 343, 185 (2001)].     

Fragmentations of isomeric sulfated monosaccharides using electrospray ion trap mass spectrometry

Electrospray ionization combined with ion trap mass spectrometry (ESI-ITMS) is a powerful tool for structural analysis of complex carbohydrates. Although its application to sulfated glycans has been limited so far, it should provide critical information, such as sulfate positions, on their structures. In this work, MS(n) spectra of nine monosulfated monosaccharides, consisting of five hexoses and four N-acetylhexosamines, were measured in negative ion mode to find basic fragmentation rules for sulfated sugars. Two pairs of positional isomers with respect to sulfation, i.e., Gal4S and Gal6S, and GalNAc4S and GalNAc6S, showed characteristic fragmentation patterns in MS(3), and could be discriminated from one another by the appearance of particular diagnostic fragment ions that characterize individual isomers. It was also demonstrated that, even if a mixture of these positional isomers was analyzed, the proportion of each species could be estimated through analysis of the abundance ratios of the diagnostic ions. However, 3-O-sulfated saccharides (Glc3S and GlcNAc3S) gave a single abundant diagnostic ion in MS(2) corresponding to the hydrogensulfate ion, [OSO(3)H](-), and this characteristic clearly differentiated them from their positional isomers. In contrast, 6-O-sulfated diastereomers consisting of two groups, Glc6S, Man6S, Gal6S, and GlcNAc6S, GalNAc6S, could not be discriminated by the types of fragment ions; however, the abundance ratios of particular fragment ions differed significantly between Glc(NAc)6S and Gal(NAc)6S. Since ESI-ITMS yielded large quantities of useful information on structures of monosulfated hexoses and N-acetylhexosamines in an extremely simple and reproducible manner, establishment of a comprehensive strategy based on ESI-ITMS(n) appears to be a promising technique for structural elucidation of sulfated complex carbohydrates.     

Alternating copolymerization of styrene and methyl α-chloroacrylate with diethylaluminum chloride

The alternating copolymerization of styrene and methyl α-chloroacrylate (MCA) with diethylaluminum chloride (Et₂AlCl) in benzene at 0°C has been investigated. The copolymer has an equimolar composition irrespective of the feed monomer composition, the copolymer yield and the amount of Et₂AlCl used. The copolymerization proceeds first very rapidly and then rather slowly after attaining a certain yield which varies proportionally to the amount of Et₂AlCl used. A maximum copolymer yield is observed at about 60% MCA feed composition. The ¹H-NMR analyses of dyad, triad, and pentad of the alternating deuterated α-d-St-MCA copolymer indicate that the configuration of this copolymer can be explained by a single parameter, coisotacticity σ(σ = 0.69). A favorable mechanism of the alternating propagation as well as of the stereoregularity control is discussed.     

Polymerization of Diallyl Alkyl Isocyanurates

Abstract

Polymerizations of several diallyl alkyl isocyanurates were investigated to explore in more detail the steric effect observed in the polymerization of triallyl isocyanurate [3, 5], as compared to its isomer triallyl cyanurate, by changing alkyl groups from methyl, propyl, hexyl, and octyl up to lauryl. The rate of polymerization, the gel point, the cyclization constant, and the primary chain length were evaluated. For example, the primary chain length increased with an increase in the bulkiness of the alkyl group as expected, although in the polymerization of diallyl lauryl isocyanurate it decreased as a reflection of reduced rate of propagation due to the enhanced steric effect arising from a very bulky lauryl group.     

Stability for linearly constrained optimization problems

We deal with finite dimensional differentiable optimization problems under linear constraints. Stability of stationary solutions under restricted perturbations of the constraints will be characterized. The restriction on the constraint perturbations is given by means of a certain rank condition; in particular, righthandside perturbations are allowed.Corresponding author.