The role of Volkov waves in laser-assisted electron momentum spectroscopy

We analyze theoretically laser-assisted electron-impact ionization of atomic hydrogen at high impact energy and large momentum transfer. Considering linearly polarized laser radiation with frequency ω=10.4 fs−1 and intensity W=4×¹⁰¹² W/cm², we describe the field-dressed hydrogen state within time-dependent perturbation theory. We find that even at such moderate field parameters the laser effects on the incident, scattered, and ejected electrons with energies of 1-2 keV can in a dramatic way influence the dependence of the field-assisted differential cross sections on the recoil proton momentum.     

Assessment of delocalized and localized molecular orbitals through electron momentum spectroscopy

Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow＇s work titled ＂Is it time to retire the hybrid atomic orbital？＂ [J. Chem. Educ. 88, 860 （2011）]. To clarify the issue, we assess the delocalized and localized molecular orbitals from an experimental view using electron momentum spectroscopy. The delocalized and localized molecular orbitals based on various theoretical models for CH4, NH3, and H20 are compared with the experimental momentum distributions. Our results show that the delocalized molecular orbitals rather than the localized ones can give a direct interpretation of the experimental （e, 2e） results.     

Monte-Carlo拟合算法及其在电子动量谱学实验数据处理中应用的研究

介绍了一种新的Monte-Carlo曲线拟合算法,由于新算法具有比其他迭代算法拟合更加稳定的优势,解决了电子动量谱学实验数据处理中遇到的电离能谱能峰叠加引起的拟合效果不佳的问题.利用VB语言编写的基于以上方法的拟合程序处理CF2Br2分子的动量谱学实验数据,与基于Levenberg-Marquardt算法的PeakFit软件处理的结果进行比较,结果明显优于后者,并由此明确的重新指认了之前动量谱学方法无法指认的CF2Br2分子的价壳层最外四个轨道4b2,2a2,4b1和6a1的排序,肯定了Hartree-Fock和外价壳层格林函数方法(OVGF)的理论计算结果,而修正了光电子谱学实验的指认.     

Electronic structure tuning and band gap opening of graphene by hole/electron codoping

A pathway to open the band gap of graphene by p-n codoping is presented according to the first principles study. Two models are used: Lithium adsorbed on Boron-doped graphene (BG) and Boron-Nitrogen (B/N) codoping into graphene. The stability of Lithium adsorbed on BG is firstly analyzed, showing that the hollow site is the most stable configuration, and there is no energy barrier from some metastable configurations to a stable one. After the p-n codoping, the electronic structures of graphene are modulated to open a band gap with width from 0.0 eV to 0.49 eV, depending on the codoping configurations. The intrinsic physical mechanism responsible for the gap opening is the combination of the Boron atom acting as hole doping and Nitrogen (Lithium) as electron doping.     

Electron coincidence spectroscopy of O2: Valence electron momentum distributions and binding energies

The binding energy spectra and momentum distributions for the valence orbital transitions of molecular oxygen have been obtained using the (e,2e) reaction at total electron energies of 400 and 1200 eV. The outer π_g orbital is found to have a wave-function which is significantly more extended in momentum space than that of the more-tightly bound π_u orbitals. This is interpreted as a consequence of the single occupancy of the anti-bonding π_g orbitals. Peaks at 39 and 47 eV are assigned to ^4,2Σ_g⁻ ion states on the basis of the observed momentum distributions. The momentum distribution and observed intensity for the 32.5 eV transition supports the assignment of 2 Π_u for this ion state. The measured relative strengths for the various Π_u and Σ_u transitions are in qualitative agreement with CI and Green's function calculations.     

中性及带电钴团簇的密度泛函理论研究

本文采用基于自旋极化的密度泛函理论系统研究了 小尺寸钴团簇的几何结构和电子结构特性。随尺寸的递增,团簇的基态几何结构由一维演变为三维的几何构型。总磁矩随尺寸的增加线性递增,并呈现奇偶交替的现象。从所研究的系统中分离一个Co原子带正电的团簇体系需要的能量相对较大。本文对体系的电子亲和能（EA）以及离化势（IP）也进行了讨论。     

密度泛函理论研究Nin,Ni±n(n=1~5)团簇的结构和电子性质简

采用基于密度泛函理论的第一性原理方法系统研究了中性及带电Ni小团簇的基态几何结构和电子结构特性.对中性Nin(n=1~5)团簇,除去一个电子对基态几何结构所引起的变化相比增加一个电子所引起的影响要更加明显.n=4时,Ni+4,Ni4以及Ni-4较之相邻个体具有较大的能隙,但在所讨论的尺寸范围内,没有找到幻数结构.随着原子数的递增,Ni+n,Nin,Nin(n=1~5)团簇体系的磁矩总体呈上升趋势,值得关注的是:添加一个电子能够显著增强中性体系的磁性.讨论了与实验结论符合较好的绝热电子亲和能(AEAs)以及绝热离化势(AIPs).     

Doping golden clusters: MAu19 and M2Au18 (M = Cu and Na)

The structural and electronic properties of MAu⁻₁₉ and M₂Au⁻₁₈ (M = Cu and Na) have been studied by the relativistic density-functional calculations. It is found that the most stable configurations of CuAu⁻₁₉ and Cu₂Au⁻₁₈ are the face-centered and two-face-centered doped structures based upon the tetrahedral structure Au⁻₂₀. In contrast, the ground states of Na-doped gold clusters (NaAu⁻₁₉ and Na₂Au⁻₁₈) exhibit flat-cage configurations. The PES of these ground states are depicted that may be helpful to identify their configurations in the future experiments. The face-centered and two-face-centered doped tetrahedral structures of CuAu⁻₁₉ and Cu₂Au⁻₁₈ have a large HOMO–LUMO gap, indicating that they are chemically stable.     

Angle-resolved photoemission spectroscopy study on iron-based superconductors

Angle-resolved photoemission spectroscopy （ARPES） has played an important role in determining the band structure and the superconducting gap structure of iron-based superconductors. In this paper, from the ARPES perspective, we briefly review the main results from our group in recent years on the iron-based superconductors and their parent compounds, and depict our current understanding on the antiferromagnetism and superconductivity in these materials.     

High-resolution rotational spectroscopy of iminosilylene,HNSi

By means of Fourier transform microwave spectroscopy of a supersonic beam, the fundamental rotational transition of isotopic and vibrationally excited iminosilylene, HNSi, has been detected. In addition to seven isotopic species, vibrational satellite transitions from more than 30 vibrationally excited states, including the three fundamental modes, have been detected. Those from ν₂ are particularly intense, enabling detection of transitions from as high as (0,22⁰,0) (i.e. ～10,000 cm^?1 above ground). At high spectral resolution, well-resolved nitrogen quadrupole structure has been observed in nearly every transition. Excitation of ν₁ or ν₃ changes eQq(N) little, but eQq(N) systematically decreases with increasing excitation of the ν₂ bend, from a value of 0.376(5) MHz for (0,0⁰,0) to ?2.257(5) MHz for (0,20⁰,0). With the large amount of new data in hand, it has also been possible to determine the leading vibration–rotation constants (α_i and γ_i) for ν₂ or ν₃ to high precision, and derive a revised semi-empirical equilibrium structure for this fundamental triatomic molecule. Various electronic and molecular properties of iminosilylene have been calculated at the coupled cluster level of theory, and these generally agree well with experiment and previous calculations. An unsuccessful search for HSiN, a highly polar isomer calculated to lie nearly 3 eV above HNSi, is also reported.     

N2价轨道的精细电子动量谱学研究

在高分辨率（ΔE=08?eV,Δp≈01a.u.）高效率的第三代电子动量谱仪上获得了N₂价轨道的电离能谱和动量谱.通过对伴线结构的电子动量谱学（EMS）研究,得到了不同伴线结构的电子动量谱,另一方面也得到了伴线结构的强度.由伴线的电子动量分布形状判断出其跃迁的主要来源,并由实验测量的伴线结构强度确定了谱因子（极强度）的大小,通过对谱因子实验值与理论计算结果的比较检验了各种理论模型的精确度. 关键词： 氮分子 价轨道 电子动量谱 电子关联效应     

Electron momentum spectroscopy of the highest occupied molecular orbitals of chlorobromomethane

The first measurement of the complete valence shell binding energy spectra of chlorobromomethane (CH₂ BrCl) is reported by (e, 2e) electron momentum spectrometer using symmetric non-coplanar geometry at an impact energy of 1200 eV plus binding energy. The experimental electron momentum profiles of the highest occupied molecular orbitals (HOMOs) are extracted and compared with Hartree-Fock (HF) and density functional theory (DFT) calculations. DFT calculation employing B3LYP hybrid functional and the large-sized basis sets provides the best agreement with the experiment.     

高分辨率电子能量损失谱在材料科学中的应用

简要介绍了FEI Titan80—300STEM扫描透射电镜中装配的Wien-filter型能量单色器(monochromator).文章特别指出,装配有能量单色器的FEI Titan80—300STEM扫描透射电镜,可以直接给出高能量分辨率（~0.1eV）的电子能量损失谱.利用高分辨电子能量损失谱,在高能损失区,对于K或L能级自然宽度(natural width of energy level)小于0.5eV的元素,可以获得更细致的的近限精细结构（energy-loss near-edge structure）,更有利于解析其电子结构;在低能损失区,可以用于精确地确定半导体材料的带隙（bandgap）以及p型掺杂引起的带隙能的变化.     

Electron momentum spectroscopy of NF3

The electronic structure of nitrogen trifluoride was investigated by combining the high-resolution electron momentum spectroscopy with the high-level calculations. The experimental binding energy spectra and the momentum distributions of each orbital were compared with the results of Hartree-Fock, density functional theory （DFT）, and symmetry-adapted- cluster configuration-interaction （SAC-CI） methods. SAC-CI and DFT-B3LYP with the aug-cc-pVTZ basis set can well reproduce the binding energy spectra and the observed momentum distributions of the valence orbitals except 1 a2 and 4e orbitals. It was found that the calculated momentum distributions using DFT-B3LYP are even better than those using the high-level SAC-CI method.     

Two- and three-photon spectroscopy of solids under high pressure

Abstract

The present article reviews measurements under hydrostatic pressure on the tetrahedrally-bonded semiconductors CuCI, CuBr, ZnO, ZnS, ZnSe, ZnTe, Cds, and AgGaS₂, by two-photon spectroscopy and on the alkali halides NaC1, KBr, KI, and RbI by two- and three-photon spectroscopy. It is shown that these nonlinear techniques yield a much higher precision than linear spectroscopy in the determination of the pressure dependence of the electronic band gap. Additionally, it is often possible to determine the pressure dependence of other parameters of the electronic band structure like exciton binding energy, spin-orbit coupling, crystal-field interaction, and Luttinger parameters. In the case of the alkali halides with their rather large band gaps there is a further advantage of three-photon spectroscopy, namely that pressure-cell windows need only be transparent for photons of one third of the band gap energy.     

Bent polyynes: ring geometry studied by Raman and IR spectroscopy

Infrared (IR) and Raman spectroscopy have been used to examine the vibrational characteristics of a series of three macrocyclic tetraynes in comparison with an acyclic analog. By changing the length of the alkyl tether of the macrocycles, varying degrees of bending of the tetrayne moiety can be achieved, and the joint use of IR and Raman spectroscopies provides an avenue to probe the impact of bending on the sp‐chain. The spectroscopic data show a general trend toward decreasing activation of Raman bands in the IR spectra, and vice versa, as bending of the polyyne chain is decreased. Density functional theory calculations provide a detailed rationalization of the experimental observations. Copyright © 2011 John Wiley & Sons, Ltd.     

Sm富勒烯的价带光电子能谱

用紫外光电子能谱和同步辐射光电子能谱研究了Sm掺杂C₆₀薄膜的价带电子结构.Sm的价电子大部分转移给C₆₀，化学键以离子性为主.对于任何化学配比都没有观察到费米边，所以Sm富勒烯超导相在室温下为半导体性质.获得了很接近单相Sm_2.75C₆₀的样品在费米能级附近的电子态密度分布.固溶相的光电子发射与Sm_2.75C₆₀有明显区别.Sm_xC_{60关键词： 60}的Sm填隙化合物')" href="#">C₆₀的Sm填隙化合物 价带光电子能谱 电子结构