Investigations of a highly crowded phosphino-substituted biphenyl: A precursor for a λ3, λ5-diphosphaphenanthrene

The synthesis of 2,2′-bis(bis(dimethylamino)-phosphino)-3,3′5,5′-tetra-tert-butylbiphennyl ( 5 ) is described. It was extensively studied by ¹H, ¹³C, and ³¹P NMR spectroscopy. Furthermore, the X-ray analysis of 5 is reported. Crystals of 5 are tetragonal, space group P¯42₁c, a = b = 24.770 (3) Å, c = 12.658 (4) Å, Z = 8. The surprising reaction of 5 with proton acids leading to the formation of various phosphorus containing five- and six-membered ring compounds is discussed. On reaction of one of the six-membered ring compounds ( 9 ) with magnesium in THF, a λ³, λ⁵-diphosphaphenanthrene ( 19 ) was obtained.     

描述甲烷在Pt(110)-(21)表面的化学吸附解离的密度泛函评估

本文探讨了几种梯度近似(GGA)密度泛函及元梯度近似(meta-GGA)密度泛函在描述甲烷在重构的Pt(110)-(2×1)上的解离化学吸附作用的适用性. 金属的体相和表面结构、甲烷的吸附能量和解离能垒等被用来评估泛函的可靠性. 另外,在从头算分子动力学计算中,采用范德瓦尔斯矫正的GGA函数(optPBE-vdW)和范德瓦尔斯矫正的meta-GGA函数(MS-PBEl-rVV10）计算粘附概率. 计算结果表明,使用这两种泛函能更好地与现有的实验结果吻合,从而为发展甲烷在Pt(110)-(2×1)表面解离的可靠机器学习势能面打下重要基础.     

Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.     

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

The effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009     

The influence of contact surface microstructure on vacuum arcstability and voltage

The authors present the results of DC vacuum arc lifetime and voltage measurements for contacts with different surface microstructures. This was realized by treating the contact surface with emery paper of varying roughness. The contact surface microstructure was found to have a large effect on the DC arc lifetime (several tens of times difference at the most) and arc voltage (30% difference at the most). The mechanism of the surface microstructure effect on DC arc stability was analyzed and is explained preliminarily. The rougher the contact surface is, the longer the arc lifetime and the more stable. The arc itself has a tendency to condition the surface in a way that is unfavorable for a sustained arc lifetime. The crater size for a rough surface is smaller than for a smooth one. The rougher the contact is, the lower the arc voltage (both DC and HF components). The arc erosion has a tendency to increase the arc voltage. It is probable that type I cathode spots (fast motion, small crater size) correspond not only to the surface contamination, but also to the surface roughness