C2H4在Ru(1010)表面吸附与分解的研究

用X射线电子能谱(XPS)、热脱附谱(TDS)和紫外光电子能谱(UPS)方法研究了乙烯(C_{2H4)在Ru(1010)表面的吸附,在低温下(200K以下)乙稀(C2Ｈ4})可以在Ru(1010)表面上以分子状态稳定吸附,在200K以上乙烯(C₂H ₄)则发生了脱氢分解反应.TDS结果表明乙烯(C₂H₄)分 解后的主要产物为乙炔(C< 关键词： 乙烯 钌(1010)表面 吸附与分解     

C2H4在清洁和有Cs覆盖的Ru(0001)表面吸附的TDS研究

用热脱附谱(TDS)方法研究了乙烯(C₂H₄)在Ru(0001)表面上的吸附.在低温下(200K以下)乙烯可以在清洁及有Cs的Ru(0001)表面上以分子状态稳定吸附,在衬底温度升高至200K以上时,乙烯发生了脱氢分解反应,乙烯分解后的主要产物为乙炔(C₂H₂).在清洁的Ru(0001)表面,乙烯有两种吸附状态,脱附温度分别为275K和360K.而乙炔的脱附温度为350K.在Ru(0001)表面有Cs的存在时,乙烯分解 关键词： 乙烯 钌(0001)表面 铯钌(0001)表面乙烯 钌(0001)表面 铯钌(0001)表面     

C2H2,C2H4与K在Ru（1010）表面上共吸附的UPS研究

利用紫外光电子谱(UPS)对乙烯(C2H4)和乙烯(C2H2)气体在Ru(1010)表面的吸附及与K的共吸附进行了研究,实验结果表明：当衬底温度超过200K,乙烯即发生脱氢反应后,σCH和σCC能级均高结合方向移动．在室温下、σCH和σCC能级位置与乙炔在Ru(1010)表面的吸附时的分子能级完全一致．乙烯发生脱氢反应后的主要产物为乙炔。衬底温度从120K升到室温,Ru(1010)表面上乙炔的σCH和σCC能级均未发现变化．室温下乙炔仍然可以在Ru(1010)表面以分子状态稳定吸附．在有K的Ru(1010）表面上．室温时σCH谱峰几乎消失．碱金属K的存在促进了乙炔的分解．     

C_2H_2,C_2H_4与K在Ru(100)表面上共吸附的UPS研究

利用紫外光电子谱 (UPS)对乙烯 (C2 H4)和乙炔 (C2 H2 )气体在Ru(10 10 )表面的吸附及与K的共吸附进行了研究 ,实验结果表明 :当衬底温度超过 2 0 0K ,乙烯即发生脱氢反应后 ,σCH 和σCC 能级均向高结合能方向移动 .在室温下 ,σCH和σCC 能级位置与乙炔在Ru(10 10 )表面的吸附时的分子能级完全一致 .乙烯发生脱氢反应后的主要产物为乙炔 .衬底温度从 12 0K升到室温 ,Ru(10 10 )表面上乙炔的σCH 和σCC 能级均未发现变化 .室温下乙炔仍然可以在Ru(10 10 )表面以分子状态稳定吸附 .在有K的Ru(10 10 )表面上 ,室温时σCC谱峰几乎消失 .碱金属K的存在促进了乙炔的分解 .     

C2H2在金刚石（001）-（2×1）重构面上吸附的分子动力学模拟

利用Brenner半经验多体相互作用势和分子动力学模拟方法，研究了乙块（C₂H₂）分子在金刚石（001）-（2×1）重构表面上的碰撞动力学过程与化学吸附构型的关系.观察到C₂H₂在金刚石表面的6种吸附结构.约95％的吸附呈C₂H₂与表面形成两个σ单键的形式.讨论了轰击能量、入射位置及金刚石表面原子的空间位形对各种吸附构型形成的影响.还给出了化学吸附过程的分子快照，并讨论了C₂H₂分子与表面的能量交换关系. 关键词：     

乙烯在Ru( )表面价带电子特性研究

在200K以下乙烯（C2H4）可以在Ru（1010^-）表面上以分子状态稳定吸附,200K以上乙烯发生了脱氢分解反应生成乙炔（C2H2）。乙烯分解生成乙炔后,σCC和σCH 分子轨道能级向高结合 能方向分别移动了0.5和1.1eV。偏振角分辨紫外光电子谱（ARUPS）结果表明：在Ru(10106-)表面上,乙烯和脱氢反应后生成的乙炔分子在C－C键轴都不平行 于表面,而是沿表面&lt;0001&gt;晶向倾斜。     

C2H4/Ni(100)近边X射线吸收谱的多重散射理论研究

本文用多重散射原子集团方法计算并分析了C₂H₄/Ni(100)系统的碳K边近边X射线吸收精细结构(NEXAFS)谱,确定了乙烯吸附在Ni(100)表面上的几何结构。结果表明,乙烯是吸附在垂直桥位上的,其中碳原子与表面最近的镍原子距离是1.70?,而乙烯分子平面倾斜于表面50°,同时发现,氢和镍之间的相互作用对结构的形成有很大的作用,这些结果得到了不同途径的验证。 关键词：     

乙烯在Ru（1010）表面价带电子特性研究

在200K以下乙烯(C2H4)可以在Ru（1010）表面上以分子状态稳定吸附,200K以上乙烯发生了脱氢分解反应生成乙炔(C2H2)。乙烯分解生成乙炔后,σCC和σCH分子轨道能级向高结合能方向分别移动了0．5和1.1eV。偏振角分辨紫光电子谱（ARUPS)结果表明：在RM（1010）表面上,乙烯和脱氨反应后生成的乙炔分子的C—C键轴都不平行于表面,而是沿表面(0001)晶向倾斜。     

50—5000 eV电子被C4H8O,C5H10O2, C6H5CH3和C4H8O2散射的总截面

使用电子被C, H和O原子散射总截面的实验数据, 利用修正后的可加性规则计算了能量为50—5000eV的电子被4个复杂大分子C₄H₈O, C₅H₁₀O₂, C₆H₅CH₃和C₄H₈O₂散射的总截面, 并将计算结果与实验结果及其他理论计算结果进行了比较. 结果表明, 即 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应     

添加Fe(C5H5)2合成氢掺杂金刚石大单晶及其表征

在Ni₇₀Mn₂₅Co₅-C体系中添加含氢化合物Fe(C₅H₅)₂作为新型氢源, 利用温度梯度法, 在压力为5.5-6.0 GPa、温度为1280-1400 ℃的条件下, 成功合成出氢掺杂的宝石级金刚石大单晶. 通过傅里叶显微红外光谱发现, 随着Fe(C₅H₅)₂添加量的增加, 合成晶体中与氢相关的对应于sp³杂化C-H键的对称伸缩振动和反对称伸缩振动的红外特征峰2850和2920 cm^-1逐渐增强, 而晶体中氮含量却逐渐减少. 通过合成晶体的拉曼光谱分析发现, 金刚石的拉曼峰伴随Fe(C₅H₅)₂的添加向高频偏移, 这表明氢的进入在金刚石内部产生了压应力. 观察扫描电子显微镜图像发现, 在低含量Fe(C₅H₅)₂添加时晶体表面平滑, 而高含量添加时晶体表面缺陷增多, 且呈现出气孔状. 使用新的添加剂Fe(C₅H₅)₂作为氢源, 合成出含氢宝石级金刚石单晶, 丰富了金刚石单晶中对氢的研究内容, 也可为理解天然金刚石的形成机理提供帮助.     

Influence of the substrate structure on the bonding of chemisorbed acetylene to transition metal surfaces

The electronic spectrum of acetylene adsorbed on various transition metals has been measured by ultraviolet photoemission spectroscopy in various laboratories. At low temperatures (T < 150 K), all measurements concur in finding an electron spectrum that differs only moderately from the gas phase spectrum of acetylene. At room temperature, the electron spectrum of acetylene is reported to be similar to the low-temperature form on Ir(100) and Pt(100), but acetylene is reported to form an olefinic surface complex on Pd(111) and Pt(111) surfaces. In order to examine whether the surface structure of the substrate is responsible for the difference, we have measured the electronic spectrum of acetylene adsorbed on the Pd(100) and Ru(0001) surfaces. At 120 K, the spectrum of adsorbed acetylene is again a distorted gas phase spectrum on both surfaces. At 330 K, we find the acetylenic form (with a splitting of 2.5 eV of the σ-orbitals) on Pd(100) and an olefinic form on the basal plane of Ru. We conclude that the olefinic complex is proper to the threefold symmetry of the (111) and (0001) surfaces and the gas-like form is favored on the (100) surfaces of the fcc crystals.     

Thermal evolution of acetylene and ethylene on Pd(111)

The thermal evolution of acetylene and ethylene and their deuterated counterparts on a palladium (111) surface has been studied by high-resolution electron energy loss spectroscopy in the temperature range 150–500 K. Analysis of the vibrational spectra indicates that chemisorbed acetylene evolves at 300 K in the presence of surface hydrogen to mainly ethylidyne, CCH₃, and a small amount of residual acetylene. Spectra obtained with and without preadsorbed hydrogen provide evidence for a 〉C CH₂ intermediate in the reaction. Chemisorbed ethylene also evolves to ethylidyne after heating from 150 to 300 K but much of the ethylene desorbs. The high temperature (400–500 K) behavior of C₂H₂ and C₂H₄ involves formation of a CH species. Although a small amount of the CH species may be formed from the dehydrogenation of ethylidyne, it is found that carbon-carbon bond scission of acetylene near 400 K is the dominant mechanism in CH formation.     

Ultraviolet photoemission studies of acetylene and ethylene adsorptions on the Pt(111) surface: Correlations with LEED studies

The chemisorption of acetylene and ethylene on platinum (111) surfaces for T ≥ 300 K has been studied with ultraviolet photoelectron spectroscopy (UPS) at 21.2 eV. An activated metastable-stable acetylene transition observed recently in low-energy electron diffraction (LEED) intensity-energy profiles has been seen with the UPS spectra. The upperlying electronic levels of the metastable acetylene state are related to a shifted gas-phase acetylene spectrum. The stable acetylene state appears to involve a stronger molecule-surface interaction and probable rehybridization, consistent with the LEED analysis showing the molecule to be situated in a triangular position at covalent Pt-C distances. Ethylene is founf to dehydrogenate at room temperature to the stable acetylene species on Pt(111) surfaces.     

On the structure of chemisorbed acetylene and ethylene on Ni,Pd and Pt surfaces

Filtered He II (hv = 40.8 eV) photoemission spectra for acetylene and ethylene molecularly chemisorbed at T ～ 100 K on Ni(111), Ni(110), Pd(111) and Pt(111) have been obtained. The resulting vertical ionization potentials are presented and used within the framework of an approximate model to obtain information of the geometric structure of these molecules. Two initial state effects are discussed which are found to be important in deducing the molecular structures. These include an initial state shift of the lowest lying carbon-2s derived orbital and a metal atom induced shift of the σ_CC valence orbital for strongly distorted species. The magnitudes of both effects are estimated — the latter using Hartree — Fock LCAO calculations of Be interacting with acetylene or ethylene. The deduced geometries of chemisorbed ethylene are found to differ only slightly from those determined without considering these effects, but for acetylene two classes of structures are found. One class of structures is weakly distorted while the other is strongly distorted (～sp^2.5 hybridization). The latter structure is consistent with recent vibrational loss studies of chemisorbed acetylene on Ni(111) and Pt(111). In contrast to chemisorbed acetylene, chemisorbed ethylene on Ni shows relatively weak distortions. More subtle crystallographic and structural effects for acetylene and ethylene on (111), (100) and (110) Ni surfaces are also discussed.     

An XPS and UPS investigation of the adsorption of ethylene on the (111) surface of silver

Monolayer adsorption of pure ethylene on the (111) surface of saver at 80 K has been studied by X-ray (hv = 1486.6 eV) and ultraviolet (hv = 21.2 and 40.8 eV) photoelectron spectroscopy. The density of the adlayer is approximately 5 × 10¹⁴ molecules/cm² at saturation, multilayer formation being prohibited by the ultrahigh vacuum of the spectrometer. The molecular orbitals designated σ¹_CH, σ_CC, σ_CH and 2ss¹ by Demuth are observed at 7.0, 9.0, 10.3 and 13.6 eV below the Fermi level, respectively, but the higher lying π level is obscured by the silver d-band emission. The data are consistent with an undistorted molecule, adsorbed with the molecular axis parallel to the surface. Desorption occurs below 200 K without significant decomposition products remaining on the surface in agreement with the conventional notion that clean silver is relatively inert with respect to olefin adsorption.     

Adsorption of ethylene on the Pt(100) surface

Clean Pt(100) surfaces with bulk-like 1×1 structure, or the stable, reconstructed 5×20 structure and held at 200 or 330 K were exposed to ethylene. Ultraviolet photoemission spectroscopy identified the nature of the adsorbed species which depends on the structure and temperature of the clean surface and the amount adsorbed. It is ethylene on the 5 × 20 structure at 200 K, a vinyl radical on the same surface at 300 K up to half a monolayer, the remainder being added as acetylene; it is acetylene on the 1 × 1 surface at 330 K and a mixture of acetylene, vinyl and ethylene on the 1 × 1 surface at 200 K. Whatever the nature of the adsorbate, the surface coverage θ increased with exposure ? as $\text{(1 ? θ = C?}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}\text{)}$. By contrast, on a surface covered with any C₂ hydrocarbon acetylene adsorbs with Langmuir kinetics. The kinetics are explained in terms of the relationship between the attraction an approaching molecule experiences from the bare surface and its Van der Waals repulsion from preadsorbed molecules.     

Thermal evolution of C2H2 and C4H2 on Pd(111) studied by high-resolution electron energy loss spectroscopy

The thermal evolution of acetylene and ethylene on a palladium (111) surface has been studied by high-resolution electron energy loss spectroscopy in the temperature range 150K–500K. Formation of ethylidyne ( CCH₃) near room temperature is important for both molecules, whereas CH is the major surfaces hydrocarbon species formed at high temperatures.     

Photoemission studies of H2S,H2 and S adsorbed on Ru(110): Evidence for an adsorbed SH species

H₂S, H₂ and S adsorbed on Ru(110) have been studied by angle-integrated ultraviolet photoemission (UPS) as part of a study of the effect of adsorbed sulfur, a common catalytic poison, on this Ru surface. For low exposures of H₂S at 80 K, the work function rises to a value 0.16 eV above that of clean Ru(110) while the associated UPS spectra (hν = 21.2 eV) exhibit features similar to those of H(ads) and S(ads) and different from those of molecular H₂S. We conclude that H₂S dissociates completely at low coverages on Ru(110) at 80 K. At intermediate exposures the work function drops and the UPS spectra show new features which are attributed to the presence of an adsorbed SH species. This appears to be the first direct observation of this surface complex. At higher exposures the work function saturates at a value 0.36 eV below the clean value; the UPS spectra change markedly and indicate the adsorption of molecular H₂S. Heating adsorbed H₂S leaves a stable layer of S(ads) on Ru(110). The surface with adsorbed sulfur strongly modifies the adsorption at 80 K of a number of molecules relative to the clean Ru(110) surface.