CO与Cs在Ru(101-0)表面上的共吸附研究

CO与Cs在Ru（101－0）表面上共吸附的高分辨电子能量损失谱研究结果表明：CO在有Cs覆盖的Ru（101－0）表面上有两种吸附状态，除了与CO在清洁表面上相似的一种吸附状态以外，还有一种新的吸附状态，它的C—O伸缩振动频率比前者低得多．在CO暴露过程中，CO分子首先吸附在低C—O伸缩振动频率的状态，随着CO覆盖度的增加，两种吸附状态的C—O伸缩振动频率都向高频方向移动．两种吸附状态的C—O伸缩振动频率也与Cs的覆盖度有关．当CO覆盖度饱和后，在Cs覆盖度较高的表面上两种吸附状态的C—O伸缩振动频率相对 关键词：     

氧和一氧化碳在有序合金表面Pd{001}c(2×2)-Mn上的共吸附:生成二氧化碳的微观机制

用高分辨率电子能量损失谱研究了O_2和CO在有序合金表面Pd{θ01}c(2×2)-Ma上的共吸附.室温下,当CO的暴露量为1.0L(朗缪尔Langmuir)时,能量损失谱中位于253mcV的峰是由吸附于第一层中Pd原子顶位的CO的C—O伸缩振动引起的.继续暴露θ.1L的O_1之后,上述253meV峰的强度大大减弱.低温140K时,O_2和CO在Pd{001}C(2×2)-Mn上共吸附后测得的能量损失谱中出现了一个损失能量为285meV的新峰.在相同的CO的暴露量下,该峰的强度随预吸附的氧量的增加而增加. 关键词：     

CO在K/Cu(111)表面吸附的功函数变化

K覆盖的Cu(111)表面在室温下可吸附CO(可能是分解吸附),在K的覆盖度θ_K明显小于θ_min(θ_min≈0.18)的范围内,室温下CO的吸附使表面功函数增大。当θ_K≥θ_min时,表面功函数先减小,达一极小值后再随CO暴露量增大。这一结果可以用凝胶一平板(Jellium-slab)模型的图象很好地解释。 关键词：     

量子混沌系统本征态的统计非遍历性及其半经典极限

讨论半经典极限下circular unitary ensemble(CUE)系综本征态θ_k(j)的非遍历性质.为研究量子系统本征态在统计上的非遍历性,定义了本征态分布ρ_k(j)的一对统计函数：Φ_N(j)=∑N-1k=0ρ_k(j)²和Ψ_N(j)=∑N-1k=0ρ_k(j),以分别体现量子本征态分布的凸起与凹陷.在随机矩阵理论的框架内,数值地计算了由正交归一的 关键词：     

Cu(111)面K-O复合物的形成

本工作对室温Cu(111)面CO,O₂和K的共吸附进行研究。高分辨电子能量损失谱(HREELS)的实验结果表明:由于K的出现,室温下Cu表面上可以有分子状态的CO存在。C0与K在Cu(111)面上共吸附时,CO分子中的O可以和K形成“K-O”复合物,“K-O”复合物的形成与K在Cu表面上的状态有关。只有在K覆盖度大于0.04时,K原子出现退极化时。“K-O”复合物才被观察到。 关键词：     

MBa2Cu3O7-δ( M=Y,Sm,Gd,Eu)高温超导体的远红外反射光谱

本文报道多晶MBa₂Cu₃O_7-δ(M=Y,Sm,Gd,Eu)高温超导体的远红外反射光谱,其频率和温度范围分别为40—360cm^-1和4.2—300K。对于不同M的样品,反射光谱具有相似的结构。在测量范围内,所有样品都有5个反射峰,最低频率的两个峰均属B_1a对称类,分别对应Ba,Cu,O离子团振动以及M,O离子团振动,其余3个峰来自CU—O键的弯曲振动;另外,不同M的样品的反射率曲线都具有三处反转 关键词：     

Ru(0001)表面上O-Ru伸缩振动的覆盖度依赖特性

在Ru(0001)表面上,通过氧气以及二氧化氮气体的分解吸附,制备了具有不同氧覆盖度的氧覆盖层.高分辨电子能量损失谱的测量表明,O-Ru伸缩振动具有强烈的覆盖度依赖特性,其振动能量从低覆盖度时(θ_O→0.0)的54meV变化到高覆盖度时(θ_O=1.0)的81meV. 关键词：     

无序二元合金（NixCu1-x）表面CO吸附及对表面偏析的影响

根据计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x（x=0.4）的原子集团模型，然后按覆盖度θ=0.5，构造出了CO表面吸附的模型 ，应用Recursion方法计算了CO在（Ni_xCu_1-x）（存在偏析和不存在偏析时）合金表面不同位置（顶位和芯位）吸附的电子结构 .由此得出：1)CO在顶位吸附时较稳定；2)CO吸附使合金表面态密度峰降低，带宽加宽，使d轨道的局域性变弱；3)CO的吸附抑制了Cu 关键词： 化学吸附 表面偏析 Recursion方法 态密度     

密度泛函理论研究CO与Nin（n=1—6）团簇的相互作用

采用密度泛函理论对CO吸附在镍团簇表面进行了系统研究.结果表明,Ni_nCO团簇的最低能量结构是在Ni_n团簇最低能量结构的基础上吸附CO生长而成,CO的吸附没有改变Ni_n团簇的结构;CO分子在Ni_n团簇表面发生的是非解离性吸附,与优化的CO键长（0.1138?nm）相比,吸附后C—O键长变长（0.1180—0.1214?nm）,表明吸附后C—O键被削弱,CO分子被活化.自然键轨道分析表明,CO分子只与最近邻的Ni原子发生相互作用;CO分子与Ni原子相互作用的本质是CO分子内的杂化轨道与Ni原子3d, 4s, 4p轨道相互作用的结果. 关键词： nCO团簇')" href="#">Ni_nCO团簇 n团簇')" href="#">Ni_n团簇 平衡结构 电子性质     

NH3在Cu及其氧化表面物理吸附的光声振动谱研究

本工作采用激光光声谱对85K多晶Cu表面上NH₃分子的物理吸附进行了研究。通过监测NH₃分子伞形振动模(ν₂),发现在清洁和预吸附O的Cu表面上,相同物理吸附态NH₃分子振动谱的峰位频率和峰的半高宽度(FWHM)随覆盖度表现出不同的变化规律,对应着不同的物理吸附机理。实验结果同时表明高分辨率的光声谱在研究弱吸附体系细致结构和细微作用方面的潜力。 关键词：     

The coadsorption of potassium and co on the pt(111) crystal surface: A TDS,HREELS and UPS study

The interaction of CO with a potassium covered Pt(111) surface is investigated using thermal desorption (TDS), high resolution electron energy loss (HREELS) and ultraviolet photoelectron (UPS) spectroscopies. When submonolayer amounts of potassium are preadsorbed, the adsorption energy of CO increases from 25 to 36 kcal/mole, while substantial shifts in the site occupancy from the linear to the bridged site are observed. The CO stretching vibrational frequencies are shown to decrease continuously with either increasing potassium coverage or decreasing CO coverage. A minimum CO stretching frequency of 1400 cm^?1 is observed, indicative of a CO bond order of 1.5. The work function decreases by up to 4.5 eV at submonolayer potassium coverages, but then increases by 1.5 eV upon CO co-adsorption. The results indicate that the large adsorption energy, vibrational frequency and work function changes are due to molecular CO adsorption with a substantial charge donation from potassium through the platinum substrate and into the 2π¹_CO orbital.     

Unusually low stretching frequency for CO adsorbed on Fe(100)

For CO adsorption on Fe(100) different adsorption species are detected with high resolution EELS (electron energy loss spectroscopy) which sequentially fill in with increasing coverage. Up to ～ 350 K and low CO exposure (≦1 L), a predominant molecular species with an unusually low stretching frequency, 1180–1245 cm^?1, is detected. This unusual CO bond weakening is consistent with a “lying down” binding configuration of CO. For higher CO coverages at 110 K, further CO adsorption states with vibrational frequencies of 1900–2055 cm^?1 are populated which are due to CO bound with the molecular axis perpendicular to the surface.     

Infrared spectra and stability of CO and H2O sorption over Ag-exchanged ZSM-5 zeolite: DFT study

The infrared spectra and stability of CO and H₂O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag⁺ cation to form an σ-bond, and it accompanies by the back donation of d-electrons from Ag⁺ cation to the CO (π*) orbital as one and two CO molecules are adsorbed on Ag-ZSM-5. The free energy changes ΔG, −5.55 kcal/mol and 6.52 kcal/mol for one and two CO molecules, illustrate that the Ag⁺(CO)₂ complex is unstable at the room temperature. The vibration frequency of C-O stretching of one CO molecule bonded to Ag⁺ ion at 2211 cm⁻¹ is in good agreement with the experimental results. The calculated C-O symmetric and antisymmetric stretching frequencies in the Ag⁺(CO)₂ complex shift to 2231 cm⁻¹ and 2205 cm⁻¹ when the second CO molecule is adsorbed. The calculated C-O stretching frequency in CO-Ag-ZSM-5-H₂O complex shifts to 2199 cm⁻¹, the symmetric and antisymmetric O-H stretching frequencies are 3390 cm⁻¹ and 3869 cm⁻¹, respectively. The Gibbs free energy change (ΔGH₂O) is −6.58 kcal/mol as a H₂O molecule is adsorbed on CO-Ag-ZSM-5 complex at 298 K. The results show that CO-Ag-ZSM-5-H₂O complex is more stable at room temperature.     

SIMS study of the interaction of CO and O2 with K adsorbed on Au

SIMS was used to study the adsorption of potassium on a gold foil, and the interaction of O₂ and CO with potassium monolayers and submonolayers. The SIMS K⁺ signal decreased with increasing coverage of K in a manner which can be attributed to work function changes. Oxygen interacts readily with potassium monolayers and submonolayers. No evidence for the adsorption of CO on chemisorbed potassium was obtained. The results are compared with coadsorption studies on substrates other than gold.     

An IRAS study of CO bonding on Sn/Pt(1 1 1) surface alloys at maximal pressures of 10 Torr

The adsorption of CO on Pt(1 1 1), (2 × 2) and (√3 × √3)R30° Sn/Pt(1 1 1) surface alloys has been studied using temperature programmed desorption (TPD), low energy electron diffraction (LEED) and infrared reflection adsorption spectroscopy (IRAS). The presence of Sn in the surface layer of Pt(1 1 1) reduces the binding energy of CO by a few kcal/mol. IRAS data show two C-O stretching frequencies, ∼2100 and ∼1860 cm⁻¹, corresponding to atop and bridge bonded species, respectively. Bridge bonded stretching frequencies are only observed for Pt(1 1 1) and (2 × 2) Sn/Pt(1 1 1) alloy surfaces. A slight coverage dependence of the vibrational frequencies is observed for the three surfaces. High pressure IRAS experiments over a broad temperature range show no indication of bridge bonded CO on any of the three surfaces. Direct CO adsorption on Sn sites is not observed over the measured temperature and pressure ranges.     

Concentration dependence of steady-state fluorescence behavior of a liquid crystal molecule E7 in ethanol

The fluorescence excitation and emission spectra of a liquid crystal E7 in ethanol have been explored at a variety of concentrations from very dilute solutions (<1.0×10⁻⁷ mol/L) to concentrated solutions (>1.0×10⁻² mol/L) and also for neat E7. The result showed a strong dependence of the steady-state fluorescence behavior on E7 concentration in ethanol. The photophysical behavior has been interpreted in terms of short-range and long-range intermolecular interactions and ground-state molecular association as well as spectral changes of the fluorescence excitation and emission. The short-range intermolecular interaction characterized by the fluorescence emission band with the maximum between 376 and 385 nm gradually increases with increasing E7 concentration. On the other hand, the long-range intermolecular interaction characterized by the emission band with the maximum between 347 and 362 nm gradually decreases with increasing E7 concentration. Consequently, with increasing E7 concentration in ethanol the long-range interaction effect is reduced, whereas the short-range effect is enhanced and the monomer emission completely disappears at concentrations greater than 2.83×10⁻⁵ mol/L.     

Basic studies of the oxygen chemistry of silver: Oxygen,dioxygen and superoxide on potassium-dosed Ag(100)

The adsorption—desorption and structural properties of oxygen phases on K-dosed Ag(100) have been investigated. At 298 K, potassium enhances the sticking probability of O₂ on Ag(100) by a factor of ?100; the initial sticking probability and saturation uptake of O₂ are proportional to the potassium coverage (θ_K) for θ_K < 0.5. For θ_K < 0.5 the desorption spectra reveal the presence of three distinct oxygen species — O(a), O₂(a) and dissolved O. The dioxygen species, O₂(a), is associated with the presence of subsurface K and its identity is confirmed by isotope-mixing experiments and CO titration. For θ_K > 1.0 LEED shows the formation of two ordered structures and two additional features appear in the O₂ desorption spectra. One of these structures is ascribed to the growth of (001) oriented potassium superoxide (KO₂). The oxygen chemistry of Na and Rb-dosed Ag surfaces is compared with the results of the present work.     

Theoretical study of CO adsorption on the illuminated TiO2 (0 0 1) surface

A quantum modeling of the CO adsorption on illuminated anatase TiO₂ (0 0 1) is presented. The calculated adsorption energy and geometries of illuminated case are compared with the ground state case. The calculations were achieved by using DFT formalism and the BH and HLYP. Upon photoexcitation, an electron-hole pair is generated. Comparing of natural population in the ground state and the exited state, shows that an electron is trapped in a Ti⁴⁺ ion and a hole is localized in an oxygen ion. The photoelectron helps generation of a CO₂ molecule on the TiO₂ surface. As shown by optimization of these systems, the CO molecule adsorbed vertically on the TiO₂ (0 0 1) surface in the ground state case while the CO molecule made an angle of 134.3° to this surface at the excited state case. Based on the here used model the obtained adsorption energy was 0.36 eV which is in excellent agreement with the reported experimental value. In the present work the C-O stretch IR frequencies are calculated which are 1366.53 and 1423.16 cm⁻¹. These results are in good agreement with the earlier reported works for the surface carbonaceous compounds, and oxygenated carbon species.     

A TDS and HREELS study of CO adsorbed on a potassium promoted Fe(111) surface

The adsorption behavior of CO on a potassium promoted Fe(111) surface was investigated in the range from zero to several monolayers of preadsorbed potassium. TD spectra show that the presence of potassium decreases the amount of CO which is desorbed in the α (molecular) desorption state and increases the desorption temperature of this state. In addition, it gives rise to second, β (recombination) desorption state which is correlated to K desorption. The total CO uptake is comparable to that for the clean surface for precoverages of up to one monolayer, beyond this, however, it increases and at three potassium monolayers it is about twice the clean surface value. At K precoverages above 0.5 monolayer the initial sticking coefficient for CO is greatly reduced so that CO exposures of up to several thousand Langmuirs are required in order to saturate the surface. The three stretch frequencies which are observed in HREELS for CO adsorbed on clean Fe(111) are all affected by the presence of potassium. At potassium precoverages between zero and 0.5 monolayers these frequencies shift both in energy and relative intensity; however, between 0.5 and 1 preadsorbed potassium monolayers the spectra are greatly modified and now show only two losses in the CO stretch region. The lower-frequency one of these gives evidence for a close interaction of CO with the coadsorbed potassium.