Metal work-function changes induced by organic adsorbates: a combined experimental and theoretical study

The role of molecular dipole moment, charge transfer, and Pauli repulsion in determining the work-function change (Deltaphi) at organic-metal interfaces has been elucidated by a combined experimental and theoretical study of (CH(3)S)(2)/Au(111) and CH(3)S/Au(111). Comparison between experiment and theory allows us to determine the origin of the interface dipole layer for both phases. For CH(3)S/Au(111), Deltaphi can be ascribed almost entirely to the dipole moment of the CH(3)S layer. For (CH(3)S)(2)/Au(111), a Pauli repulsion mechanism occurs. The implications of these results on the interpretation of Deltaphi in the presence of strongly and weakly adsorbed molecules is discussed.     

Calculation of the Energy of the Interelectron Interaction in Molecules in a Basis of Slater Functions

Russian Physics Journal - A calculation of the electron interaction energy for the CH molecule with an open electron shell is performed using a basis of Slater atomic orbitals. The molecular...     

Electron-transmission study of the temporary anion states of substituted pyridines

Electron-transmission spectroscopy has been employed in a study of the temporary negative-ion states of 2-, 3- and 4-methylpyridine, 2-, 3- and 4-chloropyridine, 2-, 3- and 4-aminopyridine, 2-, 3- and 4-acetylpyridine and 2- and 4-vinylpyridine. The effect of substitution on the normally unoccupied orbitals, as well as that of replacement of a CH group by a nitrogen atom, is found to be related to the coefficient of the molecular orbital at the site of substitution. The latter effect, however, is much less pronounced for the unfilled than for the filled orbitals. We attribute this to changes in geometry of the aza derivatives and to the greater diffuseness of the anion wavefunction compared with that of the cation.A simple Hückel MO treatment, the equivalent of the LCBO method for filled orbitals, is applied to the unfilled orbitals of the vinylpyridines and acetylpyridines, and yields the energies of these short-lived anion states quite satisfactorily.     

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.     

Structure and electronic factors in benzene coordination to Cr(CO)3 and to cluster models of Ni,Pt, and Ag (111) surfaces

Bonding of benzene to a chromium tricarbonyl fragment and to cluster models of silver, nickel, and platinum (111) surfaces is found by means of molecular orbital calculations to be dominated by a benzene donation bond involving its π (e_1g) orbitals and metal d orbitals. Three-fold hollow sites on the clusters are calculated to be most stable for benzene coordination, a conclusion reached in a number of experimental studies of benzene on metal surfaces. On the Ag, Ni, and pt clusters, the benzene CH bonds are found to bend away from the surface by ?2°, 8° and 19°, respectively, a result of carbon atom hybridization to maximize overlap with metal orbitals. For benzene chromium tricarbonyl, the CH bonds are calculated to bend 3° toward the metal, compared to a 1.7° bend reported in a diffraction study. The direction and magnitude of the CH bending are shown to depend on the metal d orbital occupancy (an electronic factor) and the proximity of metal atoms in the adsorption site (a structure factor). Small Kekulé distortions are calculated for the chromium complex and for the C_3v sites on Pt(111). Finally, recent experimental studies showing a decrease in benzene adsorption energy when potassium is coadsorbed on Pt(111) may be understood to result from decreased π donation which accompanies the shift up of the metal d band with cathodic charging.     

Extended Huckel calculations on azo and azine analogues of polyacetylene

Extended Huckel calculations on the pi systems of polyazine, ?CHNNCH?_x, and polyazoethene, ?CHCHNN?_x, are reported. Two methods were used to find polymer band properties: extrapolation to infinite length of a series of long chain molecules and by the tightbinding method using a basis set derived from monomer (four atom) molecular orbitals. For both polymers in the all trans configuration, four pi bands are found with the lower two filled and the upper two empty. The band gap in polyazoethene is found to be 0.4 to 0.7 eV, while the band gap in polyazine is 1.9 to 2.3 eV implying that polyazoethene is expected to be a substantially better semiconductor than polyazine. Analysis of the long chain wave functions shows that the bonding and antibonding functions of the dimers CC and NN for polyazoethene or CN for polyazine are the appropriate orbitals to consider for describing the band properties of these polymers, and this is the starting point for the tightbinding calculation.     

苯甲醇分子HOMO和N-HOMO轨道的电子动量谱学研究

利用第三代电子动量谱仪研究了苯甲醇(C_6H_5CH_2OH)分子的最高占据轨道(HOMO)和次最高占据轨道(N-HOMO)电子动量谱,给出了外价轨道的电离能谱信息.实验在非共面对称几何条件下完成,入射电子的能量为2400 eV加结合能.通过密度泛函方法计算得到了苯甲醇分子最高和次最高占据轨道的动量谱,理论与实验结果符合较好.     

Theoretical studies on the near edge X-ray absorption fine structure spectra of a hexanethiolate monolayer on Ag(1 0 0)

A theoretical study on the S K-edge near edge X-ray absorption fine structure (NEXAFS) of a hexanethiolate monolayer on Ag(1 0 0) has been performed by employing the multiple-scattering cluster (MSC) method. The unoccupied molecular orbitals of the system, which are closely correlated with resonances of the NEXAFS spectra, have been calculated by using the discrete variational (DV)-Xα method. The physical origins of the resonances are elucidated by these theoretical studies. It has been shown that the leading peak at 2470.3 eV is not a π*(S–C), but a resonance corresponding to the transition of 1s electrons into a hybrid orbital of the S(3p) atomic orbital of a hexanethiolate molecule and Ag atomic orbitals. The interaction between the adsorbate and the substrate induces other two weak resonances at 2475.2 and 2478.2 eV in the NEXAFS. The adsorption structure of a hexanethiolate monolayer on Ag(1 0 0) deduced from the theoretical analysis on the NEXAFS is in agreement with that from the SEXAFS of the system.     

二嗪磷的NMR研究

通过¹H , ¹³C及DQF-COSY,¹³C-¹H CO SY, COLOC等NMR技术对作为中等毒性农药二嗪磷的¹H,¹³C NMR谱峰归属作了详尽的研究，以杂化轨道理论阐明了二嗪磷结构中两个乙氧基的化学环境差异及谱峰特征, 并讨论了³¹P对二嗪磷中¹H 及¹³C NMR的影响.     

Following local adsorption sites through a surface chemical reaction: CH3SH on Cu(111)

Studying the interaction of CH3SH, methanethiol, with Cu(111) as a model system, we demonstrate the ability of chemical-shift normal incidence x-ray standing wave field measurements to identify the local adsorption geometries of coadsorbed reaction products at different temperatures, a technical problem of broad chemical significance. In the present case the local geometries of four distinct S-containing adsorbate species (intact CH3SH, two thiolate (CH3S-) reaction intermediates and atomic S) are determined.     

Staircase in the electron mobility of a ZnO quantum dot assembly due to shell filling

Electron transport in an assembly of ZnO quantum dots has been studied using an electrochemically gated transistor. The electron mobility shows a stepwise increase as a function of the electron occupation per quantum dot. When the occupation number is below two, transport occurs by tunneling between the S orbitals. Transport becomes 3 times faster when the occupation number is between two and eight; tunneling now occurs between the P orbitals. Electron transport is thus critically determined by the quantum properties of the building blocks.     

Cu~+、Ag~+、Au~+与乙硫醇的气相化学反应

利用激光溅射 分子束的技术 ,结合反射飞行时间质谱计 ,研究了Cu+、Ag+、Au+与乙硫醇的气相化学反应。结果显示这三种金属离子与 (CH3 CH2 SH) n 反应形成一系列团簇离子M+(CH3 CH2 SH) n,且团簇离子尺寸不一样。Ag+、Au+与乙硫醇的反应还生成了 (CH3 CH2 SH) +n ,由此推测Cu+、Ag+、Au+与乙硫醇团簇的反应存在两种通道 ,一种通道是生成M+(CH3 CH2 SH) n,另一种是生成 (CH3 CH2 SH) +n 。Cu+、Au+与乙硫醇的反应还生成了M+(H2 S) (M =Cu、Au) ,但是实验中没有观察到Ag+(H2 S) ,理论计算表明Ag+(H2 S)很不稳定。另外 ,分析产物离子M+(CH3 CH2 SH) n 的强度发现 ,n =1～ 2之间存在明显的强度突变现象     

多种含硫溶液钝化(100)GaAs表面的实验研究

为实现GaAs表面的钝化,以Na2S、(NH4)2S、CH3CSNH2为主要研究对象,通过对比实验研究得出较为理想的湿法钝化液。通过光致发光(PL)谱研究了(NH4)2S 叔丁醇、CH3CSNH2 NH4OH、CH3CSNH2 叔丁醇三种不同含硫溶液钝化(100)GaAs表面后的发光特性。PL谱测试发现,(NH4)2S 叔丁醇饱和溶液处理过的(100)GaAs表面光致发光强度最强,PL谱的相对发光强度是未做钝化处理的10倍左右。因此得出(NH4)2S 叔丁醇饱和溶液是较为理想的(100)GaAs表面钝化液。     

Ab initio calculation of the first ionization potential in linear alkanes using exciton theory

An ab initio calculation is used to give the form of the ionization potential in the alkane series and to explain the origin of the various contributions to this potential. The question of whether the ionization relates to a σ-type orbital, composed mainly of carbon atomic orbitals, or to a π-type, composed of CH bonds, is considered. The results show a gradual evolution from a CH ionization (13·26 eV) in CH₄ to a CC ionization (10·0 eV) at the farthest limit of the series.     

Evaluation for the configurational and electronic state of SO3 adsorbed on Pt surface

We evaluate the adsorption of SO₃ molecule on the Pt (1 1 1) surface using the first-principles calculations by a slab model with a periodic boundary condition. We find that there are four stable adsorption configurations on the Pt surface, where SO₃ molecules are adsorbed above the three-fold fcc and hcp sites. In two of these configurations, S and two O atoms are bound to the Pt atoms, and in two other of them, all the three O atoms are bound to Pt surface atoms. Besides, it is found that molecular orbitals of SO₃ and those of Pt surface are hybridized in the active metal d-bands region, that the localized molecular orbitals in SO₃ are stabilized, and that the charge is transferred from Pt to S 3p by SO₃ adsorption on Pt surface though the other interaction of S and O (bound to Pt) component with Pt is little. In addition, the bond between S and O bound to Pt become weak by SO₃ adsorption on Pt surface because the charge polarization to O-Pt bond weakens the bond between S and O bound to Pt. This interaction is assumed to encourage the breakage of S-O bond.     

1,8-萘啶衍生物分子结构与理论电子光谱

采用密度泛函理论B3LYP/6-31G(d)方法优化计算4种2,4-二甲基-7-氨基-1,8-萘啶衍生物分子结构,探讨了其分子结构与前线分子轨道、能量的关系。运用含时密度泛函理论(TD-DFT)计算了它们的气相和溶液相电子光谱,研究了溶剂模型和计算方法对理论光谱的影响。计算结果表明,4种萘啶衍生物均含离域π键,HOMO与LUMO能级差ΔE较小,且大小顺序与它们的最大吸收波长实验值变化趋势一致。理论电子光谱证实,1,8-萘啶衍生物的吸收光谱随共轭性增强逐渐红移, 最大吸收源自于HOMO→LUMO的π→π*电子跃迁。PCM-B3LYP/6-31+G(d)计算结果与实验值相比,最大吸收波长分别相差2.6,10.3,5.3和6.9 nm,能量相差0.03,0.09,0.04和0.08 eV。因此,在考虑溶剂效应条件下,采用B3LYP/6-31(d) 方法优化分子构型和TD-DFT方法获得的电子光谱与实验光谱具有一致性。     

Quantum beat between two excitonic levels split by spin--orbit interactions in the oxychalcogenide LaCuOS

Degenerate four-wave mixing signals excited by femtosecond laser pulses were measured in LaCuOCh (Ch = S and Se) at 4 K. The signals for LaCuOS exhibit a beat structure with a period of 480 fs just at the exciton peak energy, indicating that the lowest exciton states are split by 9 meV, but no beat structure was observed in LaCuOSe, regardless of the laser's energy. The spin--orbit interaction of the Ch ion accompanied by the hybridization of Cu 3d orbitals causes splitting of the exciton levels. Furthermore, the contribution of Ch p orbitals in the valence band maximum is larger in LaCuOSe owing to increased covalency in the Cu--Ch bond when S is replaced with Se.     

The HeI photoelectron spectra of methyl-substituted 1,2,4-pentatrienes (vinylallene)

The HeI photoelectron spectra of trans-1,2,4-hexatriene(1), 4-methyl-1,2,4-pentatriene(2), 3-methyl-1,2,4-pentatriene(3), 1,3,4-hexatriene(4) and 3,4-dimethyl-1,2,4-pentatriene(5) have been obtained and interpreted. LCBO and CNDO/S calculations indicate for the highest energy orbitals a π,π,π,σ sequence as in 1,2,4-pentatriene. The effect of methyl substitution on the three π orbitals is analyzed.     

含硫双Schiff碱型配体的合成与表征

用桥联水杨醛OHC-C6H4O-R-OC6H4-CHO[R=-(CH2)2-，-(CH2)3-，-CH2CH2OCH2CH2-，-(CH2CH2O)2CH2CH2-]与肼基二硫代甲酸酯(H2NNH-CSSCH3)反应，合成了四个含硫双Sehiff碱，并进行了元素分析和IR,1HNMR、MS的表征，确定了其结构。     

室温下基于微等离子体放电发射光谱法检测甲烷

建立了一套针板电极交流放电微等离子发生装置,以氮气作为载气,甲烷为分析气体,放电电压为1.32 kV, 放电距离为3 mm, Pt丝和Pt/MWNT复合纳米粒子修饰FTO电极为放电电极,放电频率为30 kHz,功率消耗为13 W,利用发射光谱法检测放电过程中产生的微等离子体发射光谱,用于在室温下检测甲烷气体。在交流电压下,检测到甲烷的谱线有CH,C₂和H_α,以C₂谱线作为甲烷分析线,发现C₂谱线强度与甲烷浓度在0.5%～4.0%(φ)的范围内呈线性,检出限(S/N=3)为0.19%。以H_α谱线为分析线,H_α谱线强度与甲烷浓度在0.1%～3.0 %(φ)范围内呈线性, 检测限(S /N=3)为0.03%(φ)。对于3.2%的甲烷气体,平行测定11次,在Pt/MWNT/FTO电极上以C₂谱线为分析线和以H_α谱线为分析线的相对标准偏差分别为 1.3%和1.9%。说明Pt/MWNT 纳米复合材料修饰电极提高了分析方法的重现性和精密度。以空气混合气体为稀释气体,甲烷气体放电行为与纯氮气中放电行为有较大差异,C₂峰消失,只有H_α峰存在。H_α峰强度与甲烷浓度在0.5%～4%范围内有线性相关性。与其他的光发射光谱检测系统相比,该系统装置尺寸小,制备简单且在室温下操作。