类钠离子光电子角分布的非偶极效应

基于密度矩阵理论和多组态Dirac-Fock方法,系统地研究了不同入射光子能量下类钠离子(20 Z92)3s,2p_(1/2)和2p_(3/2)子壳层的光电离过程,讨论了辐射场与电子相互作用的多极项对光电子角分布的影响,并给出了光电子角分布的偶极和非偶极参数.结果表明,非偶极项对光电子角分布的影响不仅与入射光子能量有关,而且与靶离子的原子序数、被电离电子的壳层等有着密切的关系.总体上,非偶极项对2p_(1/2,3/2)子壳层光电子角分布的影响大于对3s子壳层光电子角分布的影响;电偶极近似下,入射光子能量、靶离子核电荷数对s子壳层光电子角分布轮廓影响不大,对p子壳层光电子角分布影响较大,在高能光子入射下,低Z离子的p子壳层光电子角分布出现反常的角分布情况;考虑非偶极项之后,p子壳层的反常光电子角分布消失.     

Ar原子序列双光双电离产生光电子角分布的理论计算

基于多组态Dirc-Fock方法和密度矩阵理论,给出了原子序列双光双电离光电子角分布的计算表达式,发展了相应的计算程序.利用该程序对Ar原子3p壳层序列双光双电离过程进行了理论研究,给出了光电离的总截面、磁截面、剩余离子取向以及光电子角分布的各向异性参数与入射光子能量的函数关系.结果显示在光电离截面的Cooper极小位置附近取向参数出现极大值,而光电子角分布的各向异性参数在该位置附近出现极小值.进一步给出了33.94和55.34 eV光子能量下序列双光双电离过程中第一步的Ar原子和第二步的Ar^+离子3p壳层光电子角分布,分析了序列双光双电离光电子角分布与单光电离光电子角分布的差异.将计算结果与文献已有的数据进行了比较,具有很好的一致性.本文的研究结果对揭示光与物质相互作用的非线性动力学机制具有重要的参考价值.     

Ar原子和K+离子序列双光双电离光电子角分布的非偶极效应

基于多组态Dirc-Fock方法和密度矩阵理论,?给出了原子序列双光双电离光电子角分布的计算表达式,开发了相应的计算程序.?利用该程序计算了Ar原子和K+离子np?(n?=?2,?3)壳层的光电离截面、电偶极和非偶极角各向异性参数,?进一步给出了光电子的角分布情况.?结果表明:?在序列双光双电离中两次光电离过程相互影响...     

C原子、离子光电离过程的规律研究

 基于Dirac-Slater自洽场方法,计算了C原子及各价离子从低能到高能的光电离截面。通过各种理论计算结果的比较,分析了Kramers公式的适用性。定量地考察了多极效应和相对论效应在不同能区对光电离截面的影响,并研究了光电离截面随光子能量、壳层、电离度变化的规律。     

碳原子离子光电离截面的相对论多极计算

基于Dirac-slater自洽场方法,本文计算了C元素各价离子从低能到高能的光电离截面,考察了多极效应、相对论效应在不同能区对光电离截面的影响,并研究了光电离截面随光子能量、电离度、不同壳层变化的规律.通过各种理论计算结果的比较,分析了Kramers公式的适用性.计算中为了提高计算精度,我们采用了Grasp2程序包输出的束缚态波函数替换自洽场的波函数.     

氖原子光电子角分布的理论计算

本文利用密度矩阵理论和Racah代数推导出了光电子角分布的一般计算公式, 并在多组态Dirac-Fock方法基础上发展了计算原子光电离过程中产生的光电子角分布的相对论程序, 利用该程序对氖原子2s和2p光电子角分布的偶极和非偶极参数进行了具体计算, 所得结果与已有文献具有很好的一致性. 在此基础上, 本文讨论了光子与电子相互作用多级展开中的非偶极项以及入射光的极化性质对光电子角分布的影响.     

裸核离子与中性原子碰撞电离过程的理论研究

基于处理裸核离子与中性原子碰撞电离过程的OBKN和ECPSSR理论模型,系统计算了不同裸核离子与中性原子碰撞K壳层电子俘获截面和直接电离截面,并与其它文献已有的理论和实验结果进行了比较.研究结果表明：碰撞能量较低时,电子俘获截面大于直接电离截面,随着碰撞能量的增加,电子俘获截面和直接电离截面均是先增大后减小且直接电离截面减小地非常缓慢,高能时,直接电离截面大于电子俘获截面.当入射炮弹离子速度接近0.67倍靶原子K壳层电子速度时,电子俘获截面达到最大值,而当入射炮弹离子速度接近靶原子K壳层电子速度时,直接电离截面达到最大值.     

裸核离子与中性原子碰撞电离过程的理论研究

基于处理裸核离子与中性原子碰撞电离过程的OBKN和ECPSSR理论模型,系统计算了不同裸核离子与中性原子碰撞K壳层电子俘获截面和直接电离截面,并与其它文献已有的理论和实验结果进行了比较.研究结果表明:碰撞能量较低时,电子俘获截面大于直接电离截面,随着碰撞能量的增加,电子俘获截面和直接电离截面均是先增大后减小且直接电离截面减小地非常缓慢,高能时,直接电离截面大于电子俘获截面.当入射炮弹离子速度接近0.67倍靶原子K壳层电子速度时,电子俘获截面达到最大值,而当入射炮弹离子速度接近靶原子K壳层电子速度时,直接电离截面达到最大值.     

原子(离子)光电离过程中多级效应的理论研究

在相对论理论框架下,通过对氢及类氢离子光电离截面的理论研究,探讨了多极效应的变化规律和电偶极跃迁的适用范围.结果表明:光电离过程中的多极效应与入射光子的能量、电子离核的平均半径等密切相关.入射光子的能量对多极效应的影响在通常情况下更具普遍意义,当其能量较大时,光电离截面的理论计算必须考虑多极效应.     

碳原子离子光电离截面的相对论多极计算

基于Dirac-slater自洽场方法，本文计算了C元素各价离子从低能到高能的光电离截面，考察了多极效应、相对论效应在不同能区对光电离截面的影响，并研究了光电离截面随光子能量、电离度、不同壳层变化的规律．通过各种理论计算结果的比较，分析了Kramers公式的适用性，计算中为了提高计算精度，我们采用了Grasp2程序包输出的束缚态波函数替换自洽场的波函数。     

氮化镓材料中深能级中心光离化谱测试与分析

设计了一种可用于测试氮化镓材料深能级中心光离化截面的光谱测试方法,该方法建立在使用PID技术控制氮化镓样品中光电流变化为恒定值的基础上,结合光电流测试、霍尔效应、光强度测试等实验手段给出深能级中心光离化截面的实际值。使用该方法得到的光离化截面测试误差同光电探测器对不同入射光子的响应能力有关,光离化截面测试误差随入射光子能量增加不断增大,在入射光子能量较高的情况下,光离化截面测试误差约为8%。对氮化镓材料深能级中心光离化谱分析发现,即使在入射光子能量小于深能级同导带之间能量差2.85eV的情况下,深能级中心仍能在一定程度上吸收该能量的入射光子,表明深能级中心缺陷同周围晶格产生一定程度的耦合。     

Probing free xenon clusters from within

Inner-shell and valence-shell photoionization of van-der-Waals Xe clusters have been measured using both angle-resolved photoelectron spectroscopy and velocity map ion imaging technique. Both techniques have been used to probe the electronic properties and the fragmentation dynamics of clusters as a function of photon energy and cluster size. In particular, the evolution of the photoelectron angular distributions and partial cross sections as a function of photon energy and cluster size has revealed cluster size effects similar to the ones found in solids. Our cluster angular distribution parameters have been compared to the free atoms. In addition, the measurement of the fragmentation dynamic of the clusters seems to be photon energy dependent.     

原子核对光电离截面的影响

利用Dirac-Slater相对论平均自洽场理论,研究了不同原子体系光电离截面在不同核模型下的差异.考虑原子核大小时,核的尺寸效应使电子所感受到的有效核电荷减小,并进而影响到电子的概率分布及光电离截面等;对没有考虑原子核大小的点模型,由于不存在核的尺寸效应,出射光电子的波函数有较大相移,从而有可能出现Cooper极小.当入射光子的能量远大于相关电子的电离能时,不同核模型下电子束缚能及平均半径等的差异将相对减小,从而使光电离截面随入射光子能量的变化趋于一致.     

Photoionization of a charged exciton in a GaAs/GaAlAs corrugated quantum well

Binding energies of a charged exciton as a function of well width of a GaAs/GaAlAs corrugated quantum well are investigated. The calculations have been performed by the variational method based on a two parametric trial wave function within a single band effective mass approximation. We have also included the effect of nonparabolicity of the conduction band of GaAs. We study the spectral dependence of the charged exciton in a GaAs/GaAlAs corrugated quantum well as a function of well width. The photoionization cross section for the charged exciton placed at the center of the quantum well is computed as a function of normalized photon energy. The cross-section behavior as a function of incident energy is entirely different in the two cases of radiation being x-direction (along the growth direction) or z-direction. The interband emission energy as a function of well width is calculated and the dependence of the photoionization cross section on photon energy is carried out for the charged excitons. The resulting spectra are brought out for light polarized along and perpendicular to the growth direction. The results show that the charged exciton binding energy, interband emission energy and the photoionization cross section depend strongly on the well width. Our results are compared with the other existing literature available.     

Theory of spin polarization phenomena in atomic and molecular photoeffects

A compact invariant expression for the angular distribution of photoelectrons formed as a result of photoionization of axisymmetrically polarized atoms and molecules, including optically active molecules, is derived from the general symmetry considerations and using a recently developed bipolar harmonic reduction technique. In the angular distribution of photoelectrons, as well as in the total photoionization cross section, the dependence on all the geometric parameters is separated completely. The polarization of ionizing radiation can be arbitrary, with the partial polarization being specified by the Stokes parameters. The expression for the angular distribution of photoelectrons escaping from an atomic-molecular system oriented in the first order also determines the structure of the expression for the photoionization cross section of an unpolarized system with allowance for the spin polarization of a photoelectron or a photoion with the spin 1/2. The roles played by circular dichroism, chirality, etc., in the process of photoionization of oriented and aligned systems are analyzed in detail.     

A systematic angle-resolved photoelectron study of π orbitals in unsaturated organic molecules

The angular distribution parameter β has been determined for the π orbitals of 1,1-dichloroethylene, tetrachloroethylene, tetrafluoroethylene, propylene, 1-butene, isobutylene, cis-2-butene, trans-2-butene, 1,3-butadiene, cyclopentene, methylacetylene and furan in the photon energy range 10–30 eV using dispersed polarized synchrotron radiation. The energy dependence of β in the photoelectron energy range 2–10 eV was found to be similar for all the π orbitais investigated. The potential use of the energy dependence of β as an aid in making molecular-orbital assignments is discussed. Resonance photoionization features similar to those observed for the π orbitals of acetylene, ethylene and benzene were found in many of the π orbitals of the molecules investigated herein. Possible explanations for these resonance features are discussed.     

Spectroscopy of He–Ne afterglow plasma

Implementation of promising control schemes for the intensity and position of X-ray-laser beams with a photon energy up to several tens of kiloelectronvolts requires knowledge of the angular dependence of cross sections for photoionization of noble gas atoms by hard photons. Estimates of quadrupole corrections to the cross section for photoionization of a Kr atom by X-ray photons with an energy of about 25 keV are reported in this paper. An analytic expression for the cross section of the process is parameterized in a compact form convenient for analyzing angular distributions with an arbitrary polarization of a photon beam.