锂原子激发态光电离的R—矩阵计算

使用Ｒ－矩阵方法,采用三态密耦图象计算了锂原子激发态１ｓ＾２２ｐ＾２Ｐ的光电离截面,并给出了不同分波及不同过程的截面,计算结果揭示了光电离过程中的Ｒｙｄｂｅｒｇ系列共振,并指出在非共振区光电离截面不是单调变化的。     

Mirroring doubly excited resonances in argon

New features are revealed in the low-energy photoionization spectrum of Ar by critically combining high photon resolution and differential photoelectron spectroscopic techniques. Two LS-forbidden doubly excited resonances are seen in the 3p(-1)(3/2, 1/2) partial cross sections which exhibit mirroring profiles, resulting in complete cancellation in the total photoionization cross section, as was predicted by Liu and Starace [Phys. Rev. A 59, R1731 (1999)]. These results demonstrate that a new class of weakly spin-orbit induced, mirroring resonances should be observable in partial, but not in total, collisional cross sections involving atoms, molecules, and solids in general.     

Calculation of the cross sections for the photoionization of H2 and D2 into different vibrational states of the ion

The dependence of the electronic transition moment on the internuclear distance is explicitly taken into account in the calculation of the photoionization cross section. Thus, the partial ionization cross sections for producing different vibrational states of the residual ion are obtained without invoking the Franck-Condon factor approximation. The exact electrostatic potential of H₂⁺, as well as the two-center Coulomb field, is used in the evaluation of the continuum wave function. The result can explain fairly well the ratios of the partial cross sections measured at 584 Å. The effect of the polarization of H₂⁺ due to the departing photoelectron is also studied and found to be small as far as the relative cross section is concerned. The total photoionization cross sections of H₂ and D₂ are compared with previous results obtained by other authors.     

Photoionization of the excited He atom in Debye plasmas

We present theoretical photoionization cross sections for He 1s2s ¹S and He 1s2p ¹P states in a Debye plasma environment by the complex coordinate rotation method, using a finite L² basis set constructed from one electron Laguerre orbitals. The plasma environment is found to appreciably influence the photoionization cross sections near the ionization threshold. In this regard, the photoionization cross sections of isolated He are compared with other theoretical and experimental results. Our results are in good agreement with the previous results. A new minimum appears in the photoionization cross section curve for the metastable 1s2s ¹S state. Results are given for the S- and D-wave partial photoionization for the excited 1s2p ¹P state.     

Photoionization of synchrotron-radiation-excited atoms: separating partial cross sections by full polarization control

Resonant atomic excitation by synchrotron radiation and subsequent ionization by a tunable dye laser is used to study the photoionization of short-lived Rydberg states in Xe. By combining circular and linear polarization of the synchrotron as well as of the laser photons the partial photoionization cross sections were separated in the region of overlapping autoionizing resonances of different symmetry and the parameters of the resonances were extracted.     

Fits to new calculations of photoionization cross sections for low-Z elements

Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2 < Z < 30, Z = 36) are presented which cover the photon energy range from near threshold to 300 keV. The computer program developed by Brysk and Zerby, which is based on the single-electron model and uses screened self-consistent field and Dirac-Slater wave function data furnished by Cromer, Waber and Liberman, was used. Sufficient multipoles were included to calculate the partial cross sections within a few per cent, on the assumed model. Results for several elements are compared with other calculations and measurements of total photoionization cross sections. The results are presented in a form most convenient for calculations of opacities of hot gases.     

Al~(10+)的电子碰撞电离及有关过程

用扭曲波方法计算Al~(10+)基态在Is~22s的Is,2s电子和第一激发态Is~22p的2p电子的电离截面以及基态的总电离截面(包括内壳层激发自电离).入射电子能量(?)(即(?)以2s电离能I_(2s)为单位)为1.05,1.125,l.25,1.5,2.25,4……同时计算出了电离阈值以下的激发截面(乘以所谓态密度),实现了在电离阈值处与阈值以上电离能量微分截面光滑联接;计算了光电离截面积分值,实现了在入射电子能量趋于无穷时与电子碰撞电离截面衔接.计算结果与其他方法进行了比较. 关键词：     

Calculation of the photoionization cross sections for the ions of the rubidium isoelectronic sequence by the Dirac-Fock method

The photoionization cross sections for the ground and some excited states of 11 ions of the rubidium isoelectronic sequence from Rb through Ag¹⁰⁺ are calculated by the relativistic Dirac-Fock self-consistent field method. The energy dependence of the photoionization cross sections and the changes in the threshold values along the isoelectronic sequence are considered. The influence of the exchange effect and the choice of gauge on the calculated values of photoionization cross sections is examined. For practical use, the calculated cross sections are approximated by an analytical expression. Along with the total photoionization cross sections, the asymmetry parameter in the angular distribution of photoelectrons and the degree of their polarization are also calculated.     

Vacuum ultraviolet photoelectron spectroscopy of atoms and molecules

For a complete study of the photoionization of atoms and molecules it is essential to make use of the technique of Photoelectron Spectroscopy and the continuum characteristics of synchrotron radiation. A brief review is given of the application of the above techniques in measuring partial photoionization cross sections and the angular distribution assymetry parameter β. Selected results are given, which are compared to theoretical values.     

温稠密等离子体中Al12+离子的光电离过程

本文采用多组态Dirac-Hartree-Fock方法研究了温稠密等离子体环境中Al12+离子的光电离过程. 等离子体效应采用SM屏蔽势来模拟(Stanton和Murillo在2015年提出). 计算中固定标度温度1.3eV,在强耦合等离子体环境下,研究了等离子体密度对能级,连续态波函数以及光电离截面的影响. 通过与相同等离子体条件下的Debye-Hückel模型势计算的光电离截面对比,发现两种模型对应的结果中未同时出现势形共振峰,这是由于本文采用的屏蔽模型包含等离子体简并、有限温度对动能的梯度修正和量子交换关联效应,对光电离截面的大小和共振结构具有显著影响.     

Theoretical Studies on Photoionization Cross Sections of Solid Gold

Accurate expression for photoabsorption (photoionization) cross sections of high density system proposed recently is used to study the photoionization of solid gold. The results show that the present theoretical photoionization cross sections have good agreement both in structure and in magnitude with the experimental results of gold crystal. The studies also indicate that both the real part ε' and the imaginary part ε" of the complex dielectric constant ε, and the dielectric influence function of a nonideal system have rich structures in low energy side with a range about 50 eV, and suggest that the influence of particle interactions of surrounding particles with the photoionized particle on the photoionization cross sections can be easily investigated using the dielectric influence function. The electron overlap effects are suggested to be implemented in the future studies to improve the accuracy of theoretical photoionization cross sections of a solid system.     

Experimental link of photoionization of Sc2+ to photorecombination of Sc3+: an application of detailed balance in a unique atomic system

The principle of microscopic time reversal of physical processes, detailed balance, is widely used and depended upon in the theoretical community as a connection between photorecombination (PR) and photoionization (PI). This paper reports on a novel use of detailed balance and the comparison of experimental results obtained by two very distinct techniques to determine both the metastable fraction of an ion beam and partial Sc3+ PR cross sections and partial Sc2+ PI cross sections for the ground state and for two metastable states. The Sc2+ to Sc3+ system presents a unique opportunity to obtain comprehensive state-selective information by combining results from PR and PI experiments.     

原子分子真空紫外光吸收和光电离绝对截面的精确测量

介绍了一种精确测量原子分子真空紫外光吸收和光电离绝对截面的实验方法。该方法的主要特点是使用圆筒形多级电极，有效地收集光电离产生的电子和离子，并利用高通量的同步辐射作光源，精确地测量分子（原子）的绝对光吸收、光电离和光离解截面，以及光电离量子产率和光学振子强度分布等。利用该方法获得了Ｘｅ原子和Ｎ２分子的一些实验结果。     

高密度体系光电离截面新表达式的应用

利用实验光谱学的Beer Lambert定律和介质中的麦克斯韦方程组，建立了精确的光吸收（光电离）截面表达式，并通过一个随体系粒子数密度和宏观复介电常数而变化的变换函数，将严格截面公式与Fano和Cooper 1968年建立的理想气体的光电离截面公式直接联系起来.建议：1)当知道某密度下正确的体系宏观复介电常数β,γ时，可直接由严格表达式求得高密度下非理想状态的正确光电离截面；2)或当知道该体系的粒子微观极化率η,ζ和其理想气体的精确截面时，用上述变换公式间接求得其他密度时的光电离截面.对氩原子和氙原子的应用表明：当缺乏β,γ时，可由某一合理的宏观电极化率物理（例如克劳修斯-莫索缔）模型来计算β,γ，从而获得高密度体系的截面.这样获得的结果符合被散射物质的光电离（光吸收）截面随体系粒子数密度增大而增加的客观散射现象.而且，考虑了高密度真实体系中粒子间相互作用的宏观电极化率模型越正确，如此求得的散射截面的误差就越小. 关键词： 光电离截面 光吸收截面 介电常数 极化率     

光电过程原子能级截面大量计算的实现

在ＨＦＲ方法的基础上，考虑束缚组态间的相互作用，解决了Ｃｏｗａｎ程序光电计算过程中小能量区间误差偏大及一次计算自由电子能量范围受限制的问题，确定了阈能点的计算方式，从而使大量计算成为可能．分析证明了计算结果的正确性并估计了计算精度．并对锂、钠与铯原子计算的结果与参考文献做了比较，从理论上分析了能极水平光电截面求和后的结果与轨道水平光电截面的过渡关系与差别．     

Interference effects on the photoionization cross sections between two neighbouring atoms: nitrogen as an example

Interference effects on the photoionization cross sections between two neighbouring atoms are considered based on the coherent scattering of the ionized electrons by the two nuclei when their separation is less than or comparable to the de Broglie wave length of the ionized electrons. As an example, the single atomic nitrogen ionization cross section and the total cross sections of two nitrogen atoms with coherently added photoionization amplitudes are calculated from the threshold to about 60~\AA (1~\AA=0.1~nm) of the photon energy. The photoionization cross sections of atomic nitrogen are obtained by using the close-coupling R-matrix method. In the calculation 19 states are included. The ionization energy of the atomic nitrogen and the photoionization cross sections agree well with the experimental results. Based on the R-matrix results of atomic nitrogen, the interference effects between two neighbouring nitrogen atoms are obtained. It is shown that the interference effects are considerable when electrons are ionized just above the threshold, even for the separations between the two atoms are larger than two times of the bond length of N₂ molecules. Therefore, in hot and dense samples, effects caused by the coherent interference between the neighbours are expected to be observable for the total photoionization cross sections.     

Importance of Relativistic Effects for Intermediate-Z Elements： Photoionization Process of Excited Na

Using a modified R-matrix code, the fine-structure-resolved partial photoionization cross sections of excited Na （Z = 11） are calculated within the Breit-Pauli approximation. Our calculated energy levels of Na＋ and Na are in good agreement with the experimental values within 1% and the branching ratios of the J-resolved partial cross sections are consistent with the recent measurements within the experimental uncertainties. The agreements are impossible to be obtained without adequately taking into account the relativistic effects and the electron correlations together. Therefore, even for the intermediate-Z elements （e.g. Na with Z = 11）, the relativistic effects （mainly the spin-orbit interactions） should not be neglected.     

高离化态Au离子光电离过程的理论研究

基于多组态Dirac-Fock方法的程序包GRASP92和RATIP及在此基础上最新发展的RELPHOTO08程序, 系统地研究了高离化态金离子M壳层的光电离截面随入射光子能量、 离化度以及壳层的变化规律。结果表明: 光电离截面随光子能量的增大而单调减小; 电离nl电子时, 如果相关电子的主量子数较大, 则该电子存在与否对其光电离截面几乎没有影响; 在同一离化度下, 角量子数l可引起两种性质不同的效应, 其相互竞争可导致光电离截面随入射光子能量的复杂变化。Based on multiconfiguration Dirac Fock method and the corresponding packages GRASP92 and RATIP, as well as the newly developed RELPHOTO08, the variations of M subshell photoionization cross sections with the photon energy, ionization degree and subshells for highly charged gold ions are studied systemically. The present results show that the cross sections are decreasing monotonously with the photon energy; for the photoionization of nl electrons, if the principal quantum number of removed electron is large enough, the cross sections are essentially unchanged upon the presence or absence of outer electrons; for same ionization degree, the angular quantum number introduces two opposite effects which could exist simultaneously, and the intricate variations of cross sections with the photon energy originate from the competition between these two different effects.     

相对论小分量波函数对原子光电离截面的影响

利用相对论平均自洽场理论,　研究了相对论波函数的小分量对原子光电离截面的影响。原子核尺寸效应将使波函数小分量对原子光电离截面的影响减弱。由于波函数沿径向空间被压缩,　电子离核的平均半径较小,　波函数小分量对高离化态离子光电离截面的影响比对一般原子要强得多。波函数小分量反映了相对论效应的基本特征,　从而也定性地说明了光电离过程中相对论效应的强弱。The effects of relativistic small radial component on atomic photoionization cross sections have been studied within relativistic average self consistent field theory. Relativistic effects are relatively unimportant for low photon energy, along with a review of high energy photoionization the relativistic effects are quite important. The effects of relativistic small radial component on photoionization process should show breakdown when the nuclear finite size effects is taken into account. The compression of wavefunction into the space near nucleus is so strong in highly charged ions that the electronic radius greatly decreases, and the effects of relativistic small radial component on photoionization cross sections turn to stronger than ordinary atoms. Since relativistic effects are extremely sensitive to the behavior of small radial component, the results are in good agreement with relativistic effects on photoionization cross section.     

Theoretical study of photoionization of the isoelectronic sequence Rb<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>, and Y<Superscript>3+</Superscript>

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb⁺, Sr²⁺, and Y³⁺ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb⁺, Sr²⁺, and Y³⁺ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/?)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb⁺, Sr²⁺, and Y³⁺, as well as the distinction between the shapes of the 4s-6p _1/2 mirror resonance in the partial 4p _1/2 and 4p _3/2 photoionization cross sections for the Y³⁺ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb⁺ and Sr²⁺.