H_2O在Pt(100)表面的预吸附态与高迁移性能

本文采用ASED-MO方法,计算了几O分子在Pt(100)面上不同吸附取向、不同吸附位置时的结合能,以及表面扩散激活能和扩散系数.计算结果表明,H一分子必须通过氢原子朝向衬底的预吸附态.才能进人氧原子朝向衬底的垂直顶位化学吸附状态.当Hp分子处于上述预吸附态时,势能面极为平坦,扩散系数大,迁移性高.     

H2O在SrTiO3-(001)TiO2表面上吸附和解离的密度泛函理论研究

利用密度泛函理论研究了0.25单层（ML）,0.5ML,0.75ML和1ML吸附率下H₂O在SrTiO₃-（001）TiO₂表面上的吸附行为.比较了不同吸附率下分子吸附和解离吸附的稳定性,利用微动弹性带（nudged elastic band）方法计算了H₂O的解离势垒.结果表明：在低吸附率（0.25ML和0.5ML）时,H₂O表现为解离吸附;在0.75ML吸附率下,分子吸附和解离吸附同时存在;而在全吸附（吸附率为1ML）时,分子吸附更稳定.基于对H₂O分子与表面之间以及H₂O分子之间的电荷转移和相互作用的分析,讨论了吸附率对H₂O吸附和解离的影响. 关键词： 2O')" href="#">H₂O 吸附 3-（001）TiO₂表面')" href="#">SrTiO₃-（001）TiO₂表面 密度泛函理论     

SrTiO3表面O2,H2O吸附的UPS,XPS研究

观察到还原SrTiO₃表面三价Ti离子引起的表面态的存在。分析了它在太阳光分解水中所起作用,以及光照在恢复活性中的作用。 关键词：     

H2S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论第一性原理, 在广义梯度近似下, 研究了表面覆盖度为0.25 ML (monolayer)时硫化氢分子在Fe(100)面吸附的结构和电子性质, 并与单个硫原子吸附结果进行了对比. 结果表明: 硫化氢分子吸附在B2位吸附能最小为-1.23 eV, 最稳定, B1位吸附能最大为-0.01 eV, 最不稳定; 并对硫化氢分子在B1位和B2位吸附后的电子态密度进行了分析, 也表明了吸附在B2位稳定, 且吸附在B2位后硫化氢分子几何结构变化不大; 将硫化氢中硫原子吸附与单个硫原子吸附的电子性质进行了比较, 发现前者吸附作用非常微弱; 同时对吸附后的Fe(100)面进行了对比, 单个硫原子吸附的Fe(100)面电子态密度出现了一系列峰值且离散分布, 生成了硫化亚铁, 表明在硫化氢环境下, 主要是硫化氢析出的硫原子发生了吸附. 关键词： 第一性原理 Fe(100)表面 吸附能 硫化氢     

O2、 CO2和H2O在UN(001)表面化学吸附的密度泛函理论研究

采用广义梯度近似GGA,修正Perdew-Burke-Ernzerhof交换-关联泛函,以及周期性切片模型对O₂、CO₂和H₂O在UN(001)表面的化学吸附行为进行非自旋极化水平的密度泛函理论计算. 在四个对称性化学位置条件下,对化学吸附能与分子和UN(001)表面之间距离的关系曲线进行优化. 结果表明O₂、CO₂和H₂O分子的最稳定吸附位置分别为桥式平行、空心平行和桥式H     

H2 分子在Li3N(110)表面吸附的第一性原理研究

采用第一性原理方法研究了H₂分子在Li₃N(110)晶面的表面吸附. 通过研究H₂/Li₃N(110)体系的吸附位置、吸附能和电子结构发现: H₂分子吸附在N桥位要比吸附在其他位置稳定,此时在Li₃N(110)面形成两个-NH基,其吸附能为1.909 eV,属于强化学吸附;H₂与Li₃N(110)面的相互作用主要是H 1s轨道与N 关键词： 第一性原理 3N(110)')" href="#">Li₃N(110) 2')" href="#">H₂ 吸附和解离     

紫光化合物［Cd(bpdc)(phen)2(H2O)］·6H2O的合成、结构及荧光光谱研究

以2,4′-联苯二甲酸(H2bpdc)和1,10-邻菲罗啉(phen)为配体, 采用水热法合成一例三维超分子网状镉(Ⅱ)配合物［Cd(bpdc)(phen)2(H2O)］·6H2O (1)。通过单晶X射线衍射分析, 元素分析和红外光谱分析表征化合物1的结构。单晶X射线衍射分析结果表明, 化合物1属于三斜晶系, P1空间群, 中心金属Cd(Ⅱ)离子呈现六配位扭曲八面体构型, 通过两种氢键作用和π—π堆积作用形成三维超分子结构。同时, 对化合物1进行固态/溶液以及不同温度下的荧光性能测试。以350 nm为激发波长进行激发, 298 K固态时, 化合物1在390 nm处有强发射峰, 呈现紫色荧光;77 K固态时, 化合物1的荧光光谱具有两个发射谱带, 分别位于380和520 nm处, 是因为在低温时化合物1表现出精细结构。298 K时, 化合物1在DMSO溶液和CH3OH溶液中分别在380和375 nm有最大发射, 相对于固态最大发射波长发生蓝移, 呈现紫色荧光。这均是基于中心金属微扰配体中心的π*→π跃迁发射。研究了化合物1固态和溶液的荧光寿命, 化合物1荧光衰减过程包含双组分。298 K条件下, 化合物1在DMSO溶液中的寿命(τ1=1.73 μs和τ2=14.07 μs)比CH3OH溶液中的荧光寿命(τ1=1.21 μs和τ2=12.44 μs)长。此外, 77 K固态时的荧光寿命(τ1=1.96 μs和τ2=16.11 μs)长于298 K的固态荧光寿命(τ1=1.20 μs和τ2=11.34 μs), 这是因为低温条件下降低分子内部的非辐射跃迁, 从而延长固态荧光寿命。     

Pu(100)表面吸附CO2的密度泛函研究

采用广义梯度密度泛函理论的改进Perdew-Burke-Ernzerh方法结合周期性层晶模型,研究了CO₂分子在Pu（100）面上的吸附和解离.吸附能和几何构型的计算表明,CO₂以穴位C4O4构型吸附最为有利,吸附能为1.48 eV.布居分析和态密度分析表明,CO₂与Pu表面相互作用的本质主要是CO₂分子的杂化轨道2π_μ与Pu5f,Pu6d,Pu7s轨道通过强电子转移和弱重叠杂化的方式相互作用而生成了新的化学键.计算的CO₂→CO+O解离能垒为0.66 eV,解离吸附能为2.65 eV, 表明在一定热激活条件下CO₂分子倾向于发生解离性吸附.O₂,H₂,CO和CO₂在Pu （100）面吸附的比较分析表明,较低温度下的吸附强度顺序依次为O₂,CO,CO₂,H₂;较高温度下的吸附强度顺序依次为O₂,CO₂,CO,H₂. 关键词： 密度泛函理论 Pu （100） 2')" href="#">CO₂ 吸附和解离     

不同浓度FeCl3·6H2O,CuSO4·5H2O和MnCl2·4H2O溶液核磁共振横向弛豫时间研究

利用核磁共振技术,测量了不同浓度的FeCl3.6H2O,CuSO4.5H2O和MnCl2.4H2O水溶液的核磁共振信号及横向弛豫时间.实验结果表明横向弛豫时间T2与顺磁离子浓度成反比关系,并由实验结果获得了通过核磁共振横向弛豫时间测量离子浓度的方法.     

原子分子在Pt(100)表面吸附的第一性原理研究

本文系统研究了H、N、O、C、S等原子,N_2、NH_3、NO、CO等分子和CH_3、CH、CH_2和OH等自由基在Pt(100)表面的吸附.从能量上来看,吸附能力从小到大的顺序是N_2NH_3COCH_3NOHOHNCH2OSCHC.原子类吸附物中H、N、O的最稳定吸附位均为桥位,而S、C则倾向于四重空位.所研究的分子吸附物(N_2、NH3、CO、NO),N_2和NH_3有且只有一种顶位吸附结构,CO和NO均优先吸附在空位.自由基吸附物(CH、CH_2、CH_3、OH)在Pt(100)表面上的吸附,CH_3优先吸附在顶位,CH_2、OH它们的最稳定吸附位均为桥位.原子、分子和自由基吸附后,会引起Pt(100)原子层间距的改变.     

The vibrational spectrum of H2O on Si(100)

Recent EELS measurements for H₂O adsorbed on the Si(100) reconstructed surface have been interpreted on the basis of dissociation of H₂O into OH plus H. We attempt to construct a valence force potential which yields harmonic vibrational frequencies in agreement with the EELS experiments. There is some consideration of experimental intensities in the achievement of this agreement. The experimental data cannot be fitted without introducing interaction force constants into the potential energy expression, such as the force constant coupling the silicon-oxygen stretching motion and the silicon-oxygen-hydrogen bending motion.     

Vibrational study of silicon oxidation: H2O on Si(100)

The vibrational spectrum of water dissociatively adsorbed on Si(100) surfaces is obtained with surface infrared absorption spectroscopy. Low frequency spectra (< 1450 cm⁻¹ are acquired using a buried CoSi₂ layer as an internal mirror to perform external reflection spectroscopy. On clean Si(100), water dissociates into H and OH surface species as evidenced by EELS results [1] in the literature which show a Si---H stretching vibration (2082 cm⁻¹), and SiO---H vibrations (O---H stretch at 3660 cm⁻¹ and the Si---O---H bend and Si---O stretch of the hydroxyl group centered around 820 cm⁻¹). In this paper, infrared (IR) measurements are presented which confirm and resolve the issue of a puzzling isotopic shift for the Si---O mode of the surface hydroxyl group, namely, that the Si---O stretch of the O---H surface species formed upon H₂O exposure occurs at 825 cm⁻¹, while the Si---O stretch of the ---OD surface species formed upon D₂O exposure shifts to 840 cm⁻¹, contrary to what is expected for simple reduced mass arguments. The higher resolution of IR measurements versus typical EELS measurements makes it possible to identify a new mode at 898 cm⁻¹, which is an important piece of evidence in understanding the anomalous frequency shift. By comparing the results of measurements for adsorption of H¹⁶₂O, H¹⁸₂O and D₂O with the results from recently performed first-principles calculations, it can be shown that a strong vibrational interaction between the Si---O stretching and Si---O---H bending functional group vibrations of the hydroxyl group accounts for the observed isotopic shifts.     

Adsorption and decomposition of H2O on a K-covered Pt(111) surface

The adsorption of H₂O on clean and K-covered Pt(111) was investigated by utilizing Auger, X-ray and ultra-violet photoemission spectroscopies. The adsorption on Pt(111) at 100–150 K was purely molecular (ice formation) in agreement with previous work. No dissociation of this adsorbed H₂O was noted on heating to higher temperatures. On the other hand, adsorption of H₂O on Pt(111) + K leads to dissociation and to the formation of OH species which were characterized by a work function increase, an O 1s binding energy of 530.9 eV and UPS peaks at 4.7 and 8.7 eV below the Fermi level. The amount of OH formed was proportional to the K coverage for θ_K > 0.06 whereas no OH could be detected for θ? 0.06. Dissociation of H₂O occurred already at T = 100 K, with a sequential appearance of O 1s peaks at 531 and 533 eV representing OH and adsorbed H₂O, respectively. At room temperature and above only the OH species was observed. Annealing of the surface covered with coadsorbed K/OH indicated the high stability of this OH species which could be detected spectroscopically up to 570 K. The adsorption energy of H₂O coadsorbed with K and OH on Pt(111) is increased relative to that of H₂O on Pt. The work function due to this adsorbed H₂O increases whereas it decreases for H₂O on Pt(111). The energy shifts of valence and O1s core levels of H₂O on Pt + K as deduced from a comparison of gas phase and adsorbate spectra are 2.8–4.2 eV compared to ≈ 1.3–2.3 eV for H₂O on Pt (111). This increased relaxation energy shift suggests a charge transfer screening process for H₂O on Pt + K possibly involving the unoccupied 4a₁ orbital of H₂O. The occurrence of this mode of screening would be consistent with the higher adsorption energy of H₂O on Pt + K and with its high propensity to dissociate into OH and H.     

Si(100)表面电子态的总电流谱研究

用自制的总电流谱仪研究了Si(100)2×1清洁表面以及H原子饱和吸附后的Si(100)1×1-2H双氢化相表面的电子态。在清洁表面上测得的空电子态位于价带顶以上0.7eV处,而占有电子态则在价带顶以下0.25,8.4和近12eV处。在双氢化相表面上还观测到处于价带顶以下两个诱导表面态。 关键词：     

Electron-stimulated desorption of D (H) from condensed D2O (H2O) films

The electron-stimulated desorption (ESD) of D⁻ and H⁻ ions from condensed D₂O and H₂O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of ²B₁, ²A₁ and ²B₂ dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a₁ orbital. The ion yield resulting from excitation of the ²B₁ resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption.     

H2O adsorption on Ni(100): Evidence for oriented water dimers

H₂O adsorption on clean Ni(110) surfaces at T ≦ 150 K leads at coverages below $\text{θ ? 0.5}$ to the formation of chemisorbed water dimers, bound to the Ni substrate via both oxygen atoms. The linear hydrogen bond axis is oriented parallel to the [001] surface directions. With increasing H₂O coverage $\text{(θ ≧ 0.5)}$, the accumulation of further hydrogen bonded water molecules induces some modification of the dimer configuration, producing at $\text{θ ? 1}$ a two-dimensional hydrogen bonded network with a slightly distorted ice lattice structure and long range order.     

Spectroscopically determined potential energy surfaces of the H2O, H2O, and H2O isotopologues of water

Adiabatic potential energy surfaces (PESs) for three major isotopologues of water, H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O, are constructed by fitting to observed vibration-rotation energy levels of the system using the nuclear motion program DVR3D employing an exact kinetic energy operator. Extensive tests show that the mass-dependent ab initio surfaces due to Polyansky et al. [O.L. Polyansky, A.G. Császár, S.V. Shirin, N.F. Zobov, P. Barletta, J. Tennyson, D.W. Schwenke, P.J. Knowles, Science 299 (2003) 539-542.] provide an excellent starting point for the fits. The refinements are performed using a mass-independent morphing function, which smoothly distorts the original adiabatic ab initio PESs. The best overall fit is based on 1788 experimental energy levels with the rotational quantum number J = 0, 2, and 5. It reproduces these levels with a standard deviation of 0.079 cm⁻¹ and gives, when explicit allowance is made for nonadiabatic rotational effects, excellent predictions for levels up to J = 40. Theoretical linelists for all three isotopologues of water involved in the PES construction were calculated up to 26 000 cm⁻¹ with energy levels up to J = 10. These linelists should make an excellent starting point for spectroscopic modelling and analysis.     

Eu2O3在η-Al2O3和SiO2上固体-固体表面相互作用的研究

用穆斯堡尔谱和X射线衍射技术研究了Eu₂O₃在η-Al₂O₃和硅胶上的固体表面吸附。 关键词：     

Multiple vibrational excitations of H2O and D2O on Si(100)(2 × 1): A HREELS study

The HREELS (high-resolution electron energy-loss spectroscopy) spectra from H₂O and D₂O chemisorbed on the clean Si(100)(2 × 1) surface have been investigated in the energy region between about 500 and 1400 meV. For the first time, second overtones have been observed for a chemisorbed species. This observation is believed to be due to the enhancement of the O-H stretching fundamental and overtone modes because of the temporary formation of a negative ion that occurs when the incident electron is briefly trapped in a shape resonance. Additional multiple and combination modes are observed involving the resonance enhanced overtones as well as the fundamental modes. Furthermore, the dissociation energy of the hydroxyl group has been determined and found to be much larger than the actual energy needed to dissociate hydroxyl groups on the surface, indicating that the driving force for the observed atomic rearrangements is probably Si-O bond formation rather than O-H dissociation.