长脉冲激光场中H原子的阈上电离的理论研究

利用基于密度泛函理论下的窗算符技术求解含时薛定谔方法计算了H原子在长脉冲强激光场中能量谱, 并与文献[8]中的动量空间的投影技术方法的计算结果进行了比较。在文献[8]给出的最大光电子能量范围内,我们的计算结果与文献[8]中的计算结果符合得很好,但是我们的计算结果能够给出比文献[8]中能量更高的光电子能谱,光电子能量谱的变化趋势也与实际的物理过程相符。同时我们也给出了最大光电子能量与激光强度关系的经验公式,利用我们的经验公式计算的最大光电子能量与经典计算预测的最大光电子能量符合得很好,这表明们的计算方法可靠,能够给出高精度的计算结果。因此利用基于密度泛函理论下的窗算符方法能很好地用来研究H原子在长脉冲强激光场中的阈上电离的性质。     

乙醇分子的高分辨电子动量谱学研究:单个构象异构体的轨道电子动量分布

利用高分辨电子动量谱仪测量了乙醇分子外价轨道的电离能谱,通过对一系列角度关联的电离能谱进行解谱,获得了各个电离能峰对应的分子轨道电子动量分布.利用密度泛函理论方法计算了乙醇分子两种构象异构体的轨道电子动量分布,通过与实验结果进行比较,发现实验测量的电离能为14.5和15.2 eV能峰对应的电子动量分布分别与理论计算的单个构象异构体trans 8a''和gauche 9a轨道电子动量分布符合较好.     

Electron Momentum Spectroscopy of Ethanethiol Complete Valence Shell

利用(e,2e)电子动量谱学手段首次测量了乙硫醇分子全部价轨道的束缚能谱和电子动量分布. 谱仪采用非共面对称的运动学条件,入射电子能量为1.2 keV加束缚能. 实验结果与密度泛函和Hartree-Fock方法的理论计算结果基本相符. 在束缚能谱中,观察到了17.8 eV的可能的伴线,并用电子动量谱进行了研究和标识.     

异二氯乙烯价壳层轨道电子结构的电子动量谱研究

本文报道了异二氯乙烯分子价壳层轨道电子结构的电子动量谱研究.实验由一台(e,2e)电子动量谱仪在非共面对称的几何条件下开展,入射电子能量为1200 eV.实验获得了异二氯乙烯价壳层各个轨道的电离能谱和电子动量分布.采用Hartree-Fock方法和密度泛函方法结果与实验数据基本一致.研究发现,干涉效应会对2a_2和5b_2这两个Cl孤对电子轨道的电子动量分布产生显著影响.     

Experimental and theoretical investigations into the electronic structure of CF2Br2 by electron momentum spectroscopy

The binding energy spectra and electron momentum density distributions for the valence orbitals of CF₂Br₂ have been obtained by using electron momentum spectroscopy (EMS) at an impact energy of 1200 eV plus binding energy. The measured electron momentum profiles are compared with Hartree–Fock (HF) and density functional theory (DFT) calculations with different-sized basis sets. In general, the DFT-B3LYP calculation using the large basis sets of 6-311++G** and aug-cc-pVTZ fairly describe the experimental results. Moreover, the controversial orderings of the outer valence orbitals have been reassigned. The pole strength of the main ionization transition from the inner valence orbital of 1b₂ is determined.     

Role of elastic scattering in high-order above threshold ionization

We investigate the target and intensity dependence of plateau in high-order above threshold ionization(HATI) by simulating the two-dimensional(2D) momentum distributions and the energy spectra of photoelectrons in HATI of rare gas atoms through using the quantitative rescattering model. The simulated results are compared with the existing experimental measurements. It is found that the slope of the plateau in the HATI photoelectron energy spectrum highly depends on the structure of elastic scattering differential cross section(DCS) of laser-induced returning electron with its parent ion. The investigations of the long- and short-range potential effects in the DCSs reveal that the short-range potential, which reflects the structure of the target, plays an essential role in generating the HATI photoelectron spectra.     

二乙酰分子内价轨道4ag+4bu的电子动量谱学研究

在高分辨率(ΔE=115eV, Δp≈01a.u.)电子动量谱仪上获得了二乙酰分子(d iacetyl)最内价轨道4ag_g+4bu_u的电离能谱和动量谱的实验结果， 并用Hartree-Fock和密度泛函理论方法做了理论计算.实验结果与理论计算符合较好. 关键词： 二乙酰 内价轨道 电离能 电子动量谱     

Application of the Lucy-Richardson deconvolution procedure to high resolution photoemission spectra

Angle-resolved photoemission has developed into one of the leading probes of the electronic structure and associated dynamics of condensed matter systems. As with any experimental technique the ability to resolve features in the spectra is ultimately limited by the resolution of the instrumentation used in the measurement. Previously developed for sharpening astronomical images, the Lucy-Richardson deconvolution technique proves to be a useful tool for improving the photoemission spectra obtained in modern hemispherical electron spectrometers where the photoelectron spectrum is displayed as a 2D image in energy and momentum space.     

Molecular orbital momentum distributions and binding energies for H2O using an electron impact coincidence spectrometer

The construction and operation of an instrument which uses the techniques of coincidence counting and electron impact spectroscopy is reported for the study of molecular ionization at large momentum transfer in which the two outgoing electrons are detected at 45° to the incident beam. Variation of the incident energy provides binding-energy spectra for Xe, CH₄ and H₂O up to 45 eV. Alternatively variation of the azimuthal angle (symmetric, non-coplanar geometry) gives a measure of the electron momentum distribution for any selected orbital in the binding-energy spectrum. Momentum distributions for the four valence orbitals of H₂O are compared with various wavefunctions from the literature.     

碰撞阈值下氩原子非次序双电离

利用三维经典系综模型研究了碰撞阈值下氩原子的非次序双电离.计算结果表明,关联电子末态纵向动量主要分布在二、四象限,且在原点附近几乎没有分布;Ar²⁺离子末态纵向动量谱在零动量附近呈单峰结构.上述结果与实验结果 定量一致.轨迹分析表明,在碰撞阈值下,氩原子非次序双电离的微观物理机理在不同激光强度下是不相同的.当激光强度I=0.7×10¹⁴ W/cm²时,一次碰撞主导重碰撞过程.而当I=0.4×10^{14关键词： 非次序双电离 库仑引力 碰撞阈值 电子关联}     

探测二茂铁外价轨道(e,2e)反应中的扭曲波效应

利用第三代高效率电子动量谱仪,分别在600和1500 eV两种不同入射电子能量下获得了二茂铁(ferrocene)分子外价轨道的电离能谱和电子动量谱的相关实验结果.并利用非相对论与标量相对论密度泛函方法计算出了二茂铁的重叠型和交错型两种不同构象的理论动量谱.两种构象的外价轨道一一对应,理论电子动量谱基本一样.对二茂铁的外价轨道,在低动量区观测到了强烈的扭曲波效应,这与这些轨道主要由铁原子的3d轨道构成有关.通过相对论和非相对论计算结果的比较,表明相对论效应对于二茂铁的外轨道动量分布几乎没有影响. 关键词： 二茂铁分子 电子动量谱 相对论效应 扭曲波效应     

On knock-on electrons of cosmic-ray muons in condensed matter (at 12° N)

The dependence of knock-on electron probability on the momenta of muons producing the knock-on electrons in condensed matter has been investigated by using a counter controlled cloud chamber. A search has also been made on the nature of the energy spectrum of the knock-on electrons from muons in the momentum region (0.80±0.05) to (1.70±0.05) Bev/c. It appears from the results of the measurements that there is a very weak dependence of knock-on electron probability on the primary muon momentum in the investigated muon spectral region (i.e. (0.80±0.05) to (1.70±0.05) Bev/c). The angular distributions and hence the energy spectra of the emergent electrons are found to be independent of muon momentum.     

SF6电子动量谱学研究中干涉效应的观测

利用非共面对称的高效率(e,2e)电子动量谱仪测量了SF₆分子外价分子轨道的二维电子能量- 动量密度谱. 通过理论计算与实验结果的比较,发现B3LYP密度泛函理论计算结果可以较好地解释实验测量的轨道电子动量分布. 此外,对于最外层的4个来自F2p孤对电子贡献的非键分子轨道,实验上观测到非常明显的多中心干涉图样.     

High field transport properties in a GaN/AlGaN heterostructure

The drift velocity, electron temperature, electron energy and momentum loss rates of a two-dimensional electron gas are calculated in a GaN/AlGaN heterojunction (HJ) at high electric fields employing the energy and momentum balance technique, assuming the drifted Fermi–Dirac (F–D) distribution function for electrons. Besides the conventional scattering mechanisms, roughness induced new scattering mechanisms such as misfit piezoelectric and misfit deformation potential scatterings are considered in momentum relaxation. Energy loss rates due to acoustic phonons and polar optical phonon scattering with hot phonon effect are considered. The calculated drift velocity, electron temperature and energy loss rate are compared with the experimental data and a good agreement is obtained. The hot phonon effect is found to reduce the drift velocity, energy and momentum loss rates, whereas it enhances the electron temperature. Also the effect of using drifted F–D distribution, due to high carrier density in GaN/AlGaN HJs, contrary to the drifted Maxwellian distribution function used in the earlier calculations, is brought out.     

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.     

Study of valence states of the CO2 molecule by (e, 2e) momentum spectroscopy

The (e, 2e) technique has been used to measure the binding energy spectrum and the momentum distribution of the electrons in the CO₂ molecule outer orbitals. The innermost valence states 2σ_u and 3σ_g have been localized 2 eV away from each other and evidence of configuration interaction involving 3σ_g has been found. The electron momentum distributions for the various orbitals show poor agreement with the square of the Hartree-Fock wave function Fourier transform.     

Electron momentum distributions and binding energies for the valence orbitals of hydrogen bromide and hydrogen iodide

Electron binding energy spectra and momentum distributions have been obtained for the valence orbitals of HBr and HI using noncoplanar symmetric electron coincidence spectroscopy at 1200 eV. The weakly bonding inner valence ns orbitals, which have not been observed previously, have their spectroscopic (pole) strength severely split among a number of ion states. For HBr the strength of the “main” inner valence (ns) transition is 0.42±0.03 whereas for HI it is 0.37±0.04, in close agreement with the value observed for the valence s orbitals of the corresponding isoelectronic inert-gas atoms. The spectroscopic strength for the two outermost orbitals is found to be close to unity, in agreement with many-body Green's function calculations. The measured momentum distributions are compared with several spherically averaged MO momentum distributions, as well as (for HBr) with a Green's function calculation of the generalized overlap amplitude (GOA). The GOA momentum distributions are in excellent agreement with the HBr data, both in shape and relative magnitude. Not all of the MO momentum distributions are in reasonable agreement with the data. Comparison is also made with the calculated momentum distributions for Kr, Br, Xe and I.     

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.     

Metallic-like droplets produced by irradiating rare-gas clusters with free electron laser pulses

Unlike metallic elements, rare-gas atoms remain non-metallic even if they are condensed. However, once rare-gas clusters are irradiated by extreme ultraviolet free electron laser (EUV-FEL) pulses with slightly higher energy than their ionization potential, they exhibit metallic-like behaviors because the ionization takes place sequentially within the clusters owing to the huge valence electron ionization cross section in the EUV regime. In this work Ar and Xe clusters were produced by pulsed supersonic jets, and the cluster beams were crossed synchronously with focused EUV-FEL beams ejected from the SCSS test accelerator in Japan. We measured time-of-flight (TOF) mass spectra and kinetic energy distribution (KED) of daughter ions produced via Coulomb explosion by using three dimensional (3D) momentum imaging spectrometer. The metallic-like nature is evidenced not only by widely spread charge distributions within the cluster but also by enhanced positive surface charges surrounded by quasi-free electron clouds.