Structure of a CH3S monolayer on Au(111) solved by the interplay between molecular dynamics calculations and diffraction measurements

We have investigated the controversy surrounding the (sqrt[3] x sqrt[3]) R30 degrees structure of self-assembled monolayers of methylthiolate on Au(111) by first principles molecular dynamics simulations, energy and angle resolved photoelectron diffraction, and grazing incidence x-ray diffraction. Our simulations find a dynamic equilibrium between bridge site adsorption and a novel structure where 2 CH3S radicals are bound to an Au adatom that has been lifted from the gold substrate. As a result, the interface is characterized by a large atomic roughness with both adatoms and vacancies. This result is confirmed by extensive photoelectron and grazing incidence x-ray diffraction measurements.     

Electronic origin of disorder and diffusion at a molecule-metal interface: self-assembled monolayers of CH3S on Cu111

The relationship between structure, interfacial electrostatics, bonding, and dynamics of organic molecules on metals is studied using a self-assembled monolayer of methylthiolate, CH3S, on Cu(111). The flat adsorption energy landscape of CH(3)S/Cu(111) results from metal-to-molecule charge redistribution which allows for a high mobility of CH3S. This contributes a nonuniform diffuse background to Bragg scattering, which needs to be considered in diffraction analyses. Ramifications on the interpretation of experimental data and the potential impact on the design of metal-organic interfaces are discussed.     

层子模型中重子的半轻子衰变和高能中微子反应

本文从层子模型的结构观点出发,应用文献[1]中的层子与轻子的弱相互作用等效哈密顿量和文献[2]中给出的(1/2)⁺重子波函数及文献[3]中定出的参数,对(1/2)⁺重子的半轻子衰变和高能中微子的弹性和准弹性反应进行了讨论。文中得到的(1/2)⁺重子的半轻子衰变的理论结果与实验符合较好;得到的ΔS=0过程的轴矢形状因子和ν_μ+n→p+μ^-过程的截面在误差范围内均与实验相符合;得到的ΔS=1过程的轴矢形状因子和ν_μ+p→Λ+μ⁺过程的截面与目前实验给出的粗略结果也是符合的。特别需要指出的是,本文在讨论反应问题时,理论中所包含的参数全部从电磁过程定出,在给出的轴矢形状因子和截面公式中没有引进新的参数。     

Dynamics of fluctuations below a stationary bifurcation to electroconvection in the planar nematic liquid crystal N4

We fitted C(k,tau,epsilon) proportional to exp([-sigma(k,epsilon)tau] to time-correlation functions C(k,tau,epsilon) of structure factors S(k,t,epsilon) of shadowgraph images of fluctuations below a supercritical bifurcation at V(0)=V(c) to electroconvection of a planar nematic liquid crystal in the presence of a voltage V=sqrt[2]V(0)cos((2pift) [k=(p,q) is the wave vector and epsilon identical with V(2)(0)/V(2)(c)-1]. There were stationary oblique (normal) rolls at small (large) f. Fits of a modified Swift-Hohenberg form to sigma(k,epsilon) gave f-dependent critical behavior for the minimum decay rates sigma(0)(epsilon) and the correlation lengths xi(p,q)(epsilon).     

The responses of models of "high-spontaneous" auditory-nerve fibers in a damaged cochlea to speech syllables in noise

The responses of four high-spontaneous fibers from a damaged cat cochlea responding to naturally uttered consonant-vowel (CV) syllables [m], [p], and [t], each with [a], [i], and [u] in four different levels of noise were simulated using a two-stage computer model. At the lowest noise level [+30 dB signal-to-noise (S/N) ratio], the responses of the models of the three fibers from a heavily damaged portion of the cochlea [characteristic frequencies (CFs) from 1.6 to 2.14 kHz] showed quite different response patterns from those of fibers in normal cochleas: There was little response to the noise alone, the consonant portions of the syllables evoked small-amplitude wide-bandwidth complexes, and the vowel-segment response synchrony was often masked by low-frequency components, especially the first formant. At the next level of noise (S/N = 20 dB), spectral information regarding the murmur segments of the [m] syllables was essentially lost. At the highest noise levels used (S/N = +10 and 0 dB), the noise was almost totally disruptive of coding of the spectral peaks of the consonant portions of the stop CVs. Possible implications of the results with regard to the understanding of speech by hearing-impaired listeners are discussed.     

Production of Upsilon(1S) mesons from chi(b) decays in p&pmacr; collisions at sqrt

We have reconstructed the radiative decays chi(b)(1P)-->Upsilon(1S)gamma and chi(b)(2P)-->Upsilon(1S)gamma in p&pmacr; collisions at sqrt[s] = 1.8 TeV, and measured the fraction of Upsilon(1S) mesons that originate from these decays. For Upsilon(1S) mesons with p(Upsilon)(T)>8.0 GeV/c, the fractions that come from chi(b)(1P) and chi(b)(2P) decays are [27.1+/-6.9(stat)+/-4. 4(syst)]% and [10.5+/-4.4(stat)+/-1.4(syst)]%, respectively. We have derived the fraction of directly produced Upsilon(1S) mesons to be [50.9+/-8.2(stat)+/-9.0(syst)]%.     

含ME4(M＝Mo,W;E＝S,Se)单元簇合物的合成和红外谱表征

合成了一系列单立方烷Ｍ－Ｆｅ－Ｓｅ和Ｍ－Ｃｕ（Ａｇ）－Ｓ（Ｓｅ）簇合物,并用ＵＶ,ＩＲ和Ｘ－光衍射等方法对上述簇合物进行了分析。     

Solid-state 31P CP/MAS and static 65Cu NMR characterization of polycrystalline copper(I) dialkyldithiophosphate clusters

Polycrystalline tetra-nuclear Cu4[S2P(O-i-C3H7)2]4, hexa-nuclear Cu6[S2P(OC2H5)2]6, and octa-nuclear Cu8[S2P(O-i-C4H9)2]6(S) complexes were synthesized and analyzed by means of solid-state 31P CP/MAS and 65Cu static NMR spectroscopy. The symmetries of the electronic environments around each P-site were estimated from the 31P chemical shift anisotropy (CSA) parameters, Deltaaniso and eta. The 65Cu chemical shift and quadrupolar splitting parameters obtained from the experimental 65Cu NMR spectra of the polycrystalline Cu(I)-complexes are presented. A solid-state NMR approach for the elucidation of the stereochemistry of poly-nuclear Cu(I) dithiophosphate complexes, when the structural analysis of the systems by single-crystal X-ray diffraction is not readily available, is proposed.     

The structure of methylthiolate and ethylthiolate monolayers on Au(111): Absence of the (√3 × √3)R30° phase

Surface structures of self-assembled methylthiolate and ethylthiolate monolayers on Au(111) have been imaged with STM. For saturation coverage of 0.33 ML at room temperature, the well-known (√3 × √3)R30° phase routinely observed for longer chain alkanethiolates does not appear under any conditions for adsorbed methylthiolate and ethylthiolate. Instead, both thiolate species organize themselves into a well-ordered 3 × 4 structure. We thus conclude that the stable structure for saturation coverage of methylthiolate/ethylthiolate on Au(111) at RT is 3 × 4, not (√3 × √3)R30° as generally believed. For coverage less than 0.33 ML, a striped-phase with short-range order is observed for methylthiolate. Fourier transform of the STM image from the striped-phase produces a clear (√3 × √3)R30° “diffraction” pattern. This strongly indicates that the (√3 × √3)R30° diffraction pattern for methylthiolate monolayers reported in literature is likely from the striped-phase, rather than from a true (√3 × √3)R30° lattice in real space. Consequently, theoretical modeling that reproduces the (√3 × √3)R30° structure for methylthiolate monolayers should be re-examined.     

Study of Strange Quark Mass in CFL Phase

[1]M.Alford,K.Rajagopal,and F.Wilczek,Phys.Lett.B 422 (1998) 247; Nucl.Phys.B 537 (1999) 443. [2]M.Gyulassy and L.McLerran,arXiv:nucl-th/0405013;E.V.Shuryak,arXiv:hep-ph/0405066. [3]K.Rajagopal and F.Wilczek,hep-ph/0011333. [4]M.Alford,Chris Kouvaris,and K.Rajagopal,hepph/0406137. [5]Y.Nambu and G.Jona-Lasinio,Phys.Rev.122 (1961)345. [6]R.T.Cahill and C.D.Roberts,Phys.Rev.D 32 (1985)2419. [7]R.T.Cahill and Susan M.Ganner,hep-ph/9812491. [8]A.W.Steiner,S.Reddy,and M.Prakash,Phys.Rev.D 66 (2002) 094007. [9]P.Amore,M.C.Birse,J.A.McGovern,and N.R.Walet,Phys.Rev.D 65 (2002) 074005. [10]M.Alford and K.Rajagopal,JHEP 0206 (2002) 031. [11]Xiao-Fu Li,Yu-Xin Liu,Hong-Shi Zong,and En-GuangZhao,Phys.Rev.C 58 (1998) 1195. [12]H.Reinhardt,Phys.Lett.B 244 (1990) 2. [13]Steven Weinberg,The Quantum Theory of Fields,Vol.2,Cambridge University Press,Cambridge (1996) p.348.     

Measurements of the angular distributions of muons from Υ decays in pp collisions at sqrt[s] = 1.96 TeV

The angular distributions of muons from Υ(1S,2S,3S) → μ+ μ- decays are measured using data from pp collisions at sqrt[s] = 1.96 TeV corresponding to an integrated luminosity of 6.7 fb(-1) and collected with the CDF II detector at the Fermilab Tevatron. This analysis is the first to report the full angular distributions as functions of transverse momentum p(T) for Υ mesons in both the Collins-Soper and s-channel helicity frames. This is also the first measurement of the spin alignment of Υ(3S) mesons. Within the kinematic range of Υ rapidity |y|<0.6 and p(T) up to 40 GeV/c, the angular distributions are found to be nearly isotropic.     

超高泵浦功率下的Xe(6p[1/2]0, 6p[3/2]2, 和6p[5/2]2)原子的能量转移过程

本文研究了Xe(6p[1/2]₀, 6p[3/2]₂, and 6p[5/2]₂)原子在聚焦条件下的动力学过程. 激发能级的原子密度在聚焦条件下会显著地增加,因此两个高激发态原子之间的energy-pooling碰撞的概率也会增加. 这种energy-pooling碰撞主要有三种类型. 第一种类型为energy-pooling碰撞导致的电离. 一旦将激发激光聚焦,就可以从侧面的窗口观察到非常明显的电离现象,不论激发能级是6p[1/2]₀、6p[3/2]₂或6p[5/2]₂能级. 这种电离的产生机理是energy-pooling电离或者一个Xe^*原子再吸收一个光子产生电离. 第二种类型为跨越较大能极差的energy-pooling碰撞. 当激发能级为6p[1/2]₀能级的情况下,两个6p[1/2]₀原子碰撞会产生一个5d[3/2]₁原子和一个6s''[1/2]₀原子. 第三种类型为跨越较小能级差的energy-pooling碰撞. 以5个二次产生的6p能级为上能级的荧光强度都变得更强,并且这些荧光的上升沿都变得更陡峭. 产生这些6p原子的主要机理是energy-pooling碰撞并非简单的碰撞弛豫. 基于理想气体原子之间的碰撞概率公式,推导出两个6p[1/2]₀原子的energy-pooling碰撞速率为6.39x10⁸s^-1. 此外,6s原子在聚焦条件下的密度也会增加. 因此所有的荧光曲线会因为辐射俘获效应而出现非常严重的拖尾.     

Adsorption and reaction of methanethiol on the Ru(0 0 0 1)-p(2 × 2)O surface: A TPD and XPS study

Methanethiol adsorbed on Ru(0 0 0 1)-p(2 × 2)O has been studied by TPD and XPS. The dissociation of methanethiol to methylthiolate and hydrogen at 90 K is evidenced by the observation of hydroxyl and water. The saturation coverage of methylthiolate is ∼0.15 ML, measured by both XPS and TPD. A detailed analysis suggests that only the hcp-hollow sites have been occupied. Upon annealing the surface, water and hydroxyl desorb from the surface at ∼210 K. Methylthiolate decomposes to methyl radical and atomic sulphur via C-S cleavage between 350 and 450 K. Some methyl radicals (0.05 ML) have been transferred to Ru atoms before they decompose to carbon and hydrogen. The rest of methyl radicals desorb as gaseous phase. No evidence for the transfer of methyl radical to surface oxygen has been found.     

氩原子共振增强多光子电离谱--奇对称性里德堡态

利用脉冲放电产生氩原子亚稳态4s2[3/2]°2和4s′2[1/2]°0,在610～670nm波长范围内,利用共振增强多光子电离和飞行时间质谱技术得到氩原子(2+1)REMPI谱.光谱分析表明所有谱线来源于氩原子4s2[3/2]2和4s′2[1/2]°0两个亚稳态向16个奇对称性里德堡态双光子跃迁,并标识所有谱线.同时首次在实验上观察到一个长序列的3p54s′2[1/2]°0→3p5nd2[1/2]°1(n=8～31)双光子跃迁.在实验技术上,提供了一种研究惰性气体原予以及其它原子高里德堡态和自电离态的新方法.     

含MoFe3S4单元的μ2—OR或μ2—SR桥联双类立方烷簇合物的红？…

对下列含ＭｏＦｅ３Ｓ４单元的μ２－ＯＲ或μ２－ＳＲ桥联双类立方烷簇合物的红外光谱进行了研究：（Ｅｔ４Ｎ）３「Ｍｏ２Ｆｅ６Ｓ８Ｃｌ６（ＯＭｅ）３」（１）,（Ｅｔ４Ｎ）３「Ｍｏ２Ｆｅ６Ｓ８（ＳＰｈ）６（ＯＭｅ）３」（２）,（Ｂｕ４Ｎ）３「Ｍｏ２Ｆｅ６Ｓ８（ＳＰｈ）６（ＯＭｅ）３」（３）（Ｅｔ４Ｎ）３「Ｍｏ２Ｆｅ６Ｓ８（ＳＢｕ＾ｔ）６（ＯＭｅ０３」（４）ｍ,（Ｅｔ４Ｎ）３「Ｍｏ２Ｆｅ６Ｓ８（ＳＰｈ）９」     

两种手性超分子螺旋链化合物的结构、VCD和荧光分析

采用非手性物质合成了配位聚合物[C10H18CuN2O9S]n（1）和[C10H14CdN2O7S]n（2）。通过元素分析,红外光谱（IR）,热稳定性分析,荧光光谱,X射线粉末衍射（XRD）,X射线单晶衍射对其进行了分析。结构分析表明,1和2分别属于手性空间群P 65和P 6122,均在c轴方向上通过氢键形成一维超分子螺旋链。振动圆二色谱（VCD）表明两种配位聚合物都非外消旋的,分析了螺旋结构对VCD光谱影响,并对2的VCD光谱进行了理论计算,计算结果与实验相符,表明化合物手性可能来自一维超分子螺旋链。二者的固体荧光光谱分析表明：1在468nm处的宽峰为金属与配体的相互作用引起的;2在325—450nm处荧光主要由配体产生,配体与Cd的配位作用形成的刚性平面增强了荧光的强度。     

XeO~*和XeS~*的紫外发射谱

研究了Xe(6p[1/2]_0 )和Xe(6p[3/2]_2)激发态与含氧分子反应的淬灭动力学.在与N_2O和OCS分子反应中,观察到较强的XeO和XeS紫外发射,其最大强度分别在234nm和227nm,并对发射机构进行了讨论.     

Resonant double excitation observed in the near-threshold evolution of the photoexcited F K alpha satellite intensity in NaF

We present a precise measurement of the photoexcited F K alpha satellite intensity's evolution for NaF from [1s2p] double excitation threshold to saturation. A direct comparison between the observed evolution and the x-ray absorption spectrum was successfully made, and the contribution of multielectron transitions to the absorption spectrum was clearly resolved for the first time. A resonance-like feature observed in the near-threshold evolution is attributed to the [1s2p]3p(2) resonant double excitation as confirmed by calculations.     

Tin-mono-sulfide (SnS) thin films prepared by chemical spray pyrolysis with different [S]/[Sn] ratios

SnS thin films were deposited by chemical spray pyrolysis using cost-effective and low-toxicity sources materials like tin (II) chloride dihydrate and thiourea as sources of tin and sulphur, respectively. We have studied the properties of sprayed SnS thin films with [S]/[Sn] ratios were varied from 1 to 4 in order to optimize these parameters. X-ray diffraction was used for analyzing the films structure, Raman Spectroscopy for assessing the films quality and structure, scanning electron microscope (SEM) for surface morphology and energy dispersive energy (EDS) for compositional element in samples, atomic force microscopy (AFM) for the topography of surfaces and optical spectroscopy for measuring transmittances and then deducing the band gap energies. All films obtained are polycrystalline with (111) as preferential direction for films with [S]/[Sn] ratio equals to one while for [S]/[Sn] ratios from 2 to 4 the main peak becomes (101) and the (111) peak decreases in intensity. Raman spectroscopy confirms the presence of only one SnS phase without any additional parasite secondary phases. SEM images revealed that films are well adhered onto glass surface with rounded grain. AFM confirms this result being films with [S]/[Sn] = 1 the roughest and also with the largest grain size. EDS results show an improvement of stoichiometry with the increase of the [S]/[Sn] ratio. From optical analysis, it is inferred that the band gap energy decreases from 1.83 to 1.77 eV when the [S]/[Sn] ratio changes from 2 to 4.     

Characterization of two dissimilatory sulfite reductases from sulfate-reducing bacteria

Mössbauer, EPR, and biochemical techniques were used to characterize two dissimilatory sulfite reductases: desulforubidin fromDesulfovibrio baculatus strain DSM 1743 and desulfoviridin fromDesulfovibrio gigas. For each molecule of desulforubidin, there are two sirohemes and four [4Fe?4S] clusters. The [4Fe?4S] clusters are in the diamagnetic 2+ oxidation state. The sirohemes are high-spin ferric (S=5/2) and each siroheme is exchanged-coupled to a [4Fe?4S]²⁺ cluster. Such an exchange-coupled siroheme-[4Fe?4S] unit has also been found in the assimilatory sulfite reductase fromEscherichia coli/1/ and in a low-molecular weight sulfite reductase fromDesulfovibrio vulgaris/2/. For each molecule of defulfoviridin, there are two tetrahydroporphyrin groups and four [4Fe?4S]²⁺ clusters. To our surprise, we discovered that about 80% of the tetrahydroporphyrin groups, however, do not bind iron.