不同覆盖度下丙硫醇在Au(111)面吸附的理论研究

采用基于密度泛函理论的第一性原理方法研究了丙烷硫醇 (C₃H₇SH)在Au(111)面五种覆盖度(1/16, 2/16, 3/16, 4/16, 1/3) 下的未解离和解离吸附的结构、能量和吸附性质. 发现丙烷硫醇的倾斜角和吸附能均受覆盖度影响, 计算结果显示丙烷硫醇的倾斜角随着覆盖度的增大减小了6°–10°, 吸附能随覆盖度的增大减小了0.21 eV. 特别针对饱和覆盖度, 研究了三种可能的表面结构: (2√3×2√3 ight)R30°, 2√3×3和(3×3). 发现S–H键未解离时三种表面结构的吸附构型和吸附能基本一致; S–H键解离后, (2√3×2√3 ight)R30°和2√3×3结构的吸附能比以(3×3)结构的吸附能约高0.05–0.07 eV, 说明C₃H₇S在Au(111)面吸附时, 倾向于形成(2√3×2√3 ight)R30°和2√3×3结构. 此外, 采用DFT-D2方法对饱和覆盖度下C₃H₇SH分子在Au(111)面的吸附进行了范德华修正, 结果显示分子间相互作用使吸附物和Au表面的距离减小, 该相互作用对吸附能的修正值为0.53 eV, 修正后结果与实验结果接近. 关键词： 第一性原理 覆盖度 表面结构 范德华力     

Modelling the interaction in a benzene dimer

The interaction between aromatic rings is a fundamental problem in material science and biochemistry. These interactions are generally found to stabilise protein molecules and the double helical structure of DNA, and they also play an important role in the recognition processes in biological and non-biological systems. However, the complexity and variety in the structures and components of aromatic compounds are major obstacles to investigating their interactions. In this study, the simplest case of aromatic interactions, which is the interaction between two benzene rings, is modelled using a continuous approximation. Assuming a constant atomic surface density and modelling the structure of a benzene molecule as a combination of two rings, namely an inner carbon ring and an outer hydrogen ring, the van der Waals interaction between any two benzene rings can be obtained as the sum of four interactions. The major result obtained here is an analytical expression for the potential energy which can then be used to predict equilibrium configurations for two interacting benzene molecules. Moreover, we find that at sufficiently large distances between the two benzene molecules, the orientational angle φ at which the interaction energy is a minimum can be approximated by the arctan of the ratio of two separation distances in two mutually perpendicular directions.     

Solvent effects on the intrinsic enhancement factors of the triplet exciplex generated by photoinduced electron transfer reaction between eosin Y and duroquinone

The spin dynamics of the duroquinone anion radical (DQ^?-) generated by photoinduced electron transfer reactions from triplet eosin Y (³EY^2-) to DQ have been studied by using transient absorption and pulsed EPR spectroscopy. Unusual net-absorptive electron spin polarization plus net-emissive polarization were observed, suggesting the production of the triplet exciplex or contact radical pair as the reaction intermediate. The kinetic parameters and intrinsic enhancement factors of the electron spin polarization were determined in various alcoholic solvents. The net-absorptive electron spin polarization was also observed in ethanol-water mixed solvents. The solvent effects on the radical yield are analysed on the basis of a stochastic Liouville equation established for the magnetic field effects on the radical yield. The zero-field splitting constants of the triplet exciplex are estimated from the solvent viscosity dependence of the enhancement factors due to spin-orbit coupling induced depopulation of the reaction intermediate.     

Synthesis of fused imidazo azepine derivatives by sequential van Leusen/enyne metathesis reactions

A facile synthesis of fused imidazo azepine derivatives by a van Leusen/intramolecular enyne metathesis synthetic sequence is reported. The two-step reaction sequence generates compounds of significant molecular complexity from simple starting materials in an expedient fashion with good overall yields.     

Quantum signatures in the dynamics of two dipole-dipole interacting soft dimers

The quantum covariances of physically transparent pairs of observables relative to two dimers hosted in a solid matrix are exactly investigated in the temporal domain. Both dimers possess fermionic and bosonic degrees of freedom and are dipolarly coupled. We find out and describe clear signatures traceable back to the presence and persistence of quantum coherence in the time evolution of the system. Manifestations of a competition between intramolecular and intermolecular energy migration mechanisms are brought to light. The experimental relevance of our results is briefly commented.     

High-resolution liquid chromatographic separations in 400 nm deep micro-machined silicon channels and fluorescence charge-coupled device camera detection under stopped-flow conditions

We report on a study exploring the possibilities of silicon etched, flat-rectangular nano-channels for the acceleration of liquid chromatography separations. Using the shear-forces originating from a moving channel part to propagate the mobile phase flow, a mixture of two neutral coumarin dyes could be separated in less than 50 ms and with a resolution of over N=10⁶ plates/m. The obtained experimental van Deemter-plot show a good agreement with the theoretical expectations and has a minimal plate height around H=1.0 μm (k=1.5) and H=0.6 μm (k=0.5). The different steps in the fabrication of the nano-channels, and the advantages of a novel detection scheme, based on fluorescent charge-coupled device-array imaging under stopped-flow conditions, are discussed as well.     

Steric and energetic properties of the Cl-–C6H6–Arn heterocluster

The dynamics of heteroclusters containing argon, benzene and chlorine has been investigated using a recently proposed potential energy functional that takes into account both the electrostatic and the non-electrostatic contributions to the overall noncovalent interaction. Related steric and energetic properties are compared with those homologous cationic clusters.     

碳纳米管增强Nb-Si基复合材料界面应力传递的研究

基于均匀化理论,建立了碳纳米管增强Nb-Si基复合材料的代表体积元模型,并采用剪切滞后模型对碳纳米管增强Nb-Si基复合材料界面上的应力分布和传递机制进行了研究,探讨了分子间作用力、杨氏模量比β、长径比α、体积分数?等对其应力分布和传递机制的影响。结果表明,复合材料界面应力分布的变化主要集中在碳纳米管的两端,最大的应力都是分布在加载端或拔出端,然后向另一端传递;分子间作用力、杨氏模量比、长径比、体积分数等参数对界面应力的传递均有一定的影响,其中长径比和体积分数的影响最明显,体积分数为0.02时拔出端的界面剪切应力值相对于体积分数为0.0025时增大幅度达到近7倍,而长径比从200减小到50时,其应力传递距离增大了近8倍。     

The Conjugacy of Stochastic and Random Differential Equations and the Existence of Global Attractors

We consider stochastic differential equations in d-dimensional Euclidean space driven by an m-dimensional Wiener process, determined by the drift vector field f₀ and the diffusion vector fields f₁,...,f_m, and investigate the existence of global random attractors for the associated flows . For this purpose is decomposed into a stationary diffeomorphism given by the stochastic differential equation on the space of smooth flows on R^d driven by m independent stationary Ornstein Uhlenbeck processes z¹,...,z^m and the vector fields f₁,...,f_m, and a flow generated by the nonautonomous ordinary differential equation given by the vector field (_t/x)^–1[f₀(_t)+ _i=1 ¹ f_i(_t)z _t ⁱ ]. In this setting, attractors of are canonically related with attractors of . For , the problem of existence of attractors is then considered as a perturbation problem. Conditions on the vector fields are derived under which a Lyapunov function for the deterministic differential equation determined by the vector field f₀ is still a Lyapunov function for , yielding an attractor this way. The criterion is finally tested in various prominent examples.