平行电磁场中锂原子自电离的半经典分析

采用包含组合回归的扩展的闭合轨道理论计算了平行电磁场中锂原子依赖于时间的自电离谱,并用半经典的方法解释了电离过程中的混沌现象.讨论了电离电子逃逸时间谱分形结构中隐含的各韵律段的电离轨迹,并得到了轨迹的一般规律,其中特别关注由核散射产生的特殊的逃逸轨迹的性质.具体研究了磁场对锂原子自电离混沌脉冲阵列中电子逃逸轨道和逃逸时间谱的影响.结果发现随着外加磁场的增大,电离脉冲越来越复杂,混沌现象也越明显.这显示了逃逸轨道对初始条件的敏感依赖性.     

平行电磁场中高里德堡态锂原子自电离的半经典分析

利用Poincaré截面和标度回归谱理论对平行电磁场中高里德堡态锂原子自电离现象进行了半经典分析.并与相同条件下氢原子的相应性质进行比较,结果表明两者有很大不同,这主要是由于离子实散射引起的.从而表明离子实对非氢原子的混沌性质起着非常重要的作用.     

磁场中氢里德堡波包的自动关联函数

本文采用激光短脉冲激发磁场中氢原子,研究氢里德堡波包在磁场中随时间的演化.结果证实氢里德堡波包在磁场中的运动也与闭合轨道密切相关.讨论了脉冲宽度τ对自动关联函数的影响以及不同初始态下的自动关联函数.     

双平行金属板间的里德堡氢原子的动力学性质

用相空间分析方法研究了双金属板间里德堡氢原子的动力学性质.结果表明：标度变换后,其动力学行为敏感地依赖于标度能量 .当标度能量 较小时,体系是近可积的,规则的,随着标度能量的增大,体系是不可积的,运动是混沌的,电子可能被金属表面俘获.     

平行电磁场中H-光剥离电子轨道分岔现象的研究

当改变能量、位置或场强等参数时,电磁场中里德堡态的原子、分子和离子等体系将出现分岔现象,从而导致波函数在分岔点附近发散,半经典闭合轨道理论不再适用.本文分析并计算了平行电磁场中H-光剥离电子轨道的分岔现象,并采用统一近似的方法进行定域修正,从而消除了分岔点的奇异性,得到了合理的光剥离电子流的分布.     

平行电磁场中H-光剥离电子轨道分岔现象的研究

当改变能量、位置或场强等参数时,电磁场中里德堡态的原子、分子和离子等体系将出现分岔现象,从而导致波函数在分岔点附近发散,半经典闭合轨道理论不再适用.本文分析并计算了平行电磁场中的H-光剥离电子轨道的分岔现象,并采用统一近似的方法进行定域修正,从而消除了分岔点的奇异性,得到了合理的光剥离电子流的分布.     

垂直电磁场中He原子的吸收谱和回归谱的理论计算

半经典闭合轨道理论已经成功地计算了在外加磁场和平行电磁场中的里德堡原子的回归谱.但对于垂直电磁场中的里德堡原子,理论和计算都变得更为复杂.本文把闭合轨道理论推广到三维情况,采用 B.Hüpper的模型势计算了ε=-0.03,主量子数n≈ 40,m=0下He原子在垂直电磁场中的光吸收谱和回归谱,并和H原子在垂直电磁场中的回归谱作比较,突出了实散射的贡献.计算中应用了离子实散射的分区自洽迭代方法,并考虑到轨道的多次重复和离子实的多次散射效应.这是对闭合轨道理论的验证和进一步推广.     

椭球坐标下求解强磁场中的氢原子

在椭球坐标系下,采用B样条基组方法计算了磁场范围在0-1000 a.u.下氢原子低能态能量以及实验室磁场下(几个特斯拉)氢原子里德堡态的能级,并与文献中的精确结果进行了比较.对1s0态,磁场γ≤100 a.u.时,本文计算结果有12位有效数字的精度,γ=1000 a.u.时有11位有效数字的精度.对2p-1低激发态,γ≤100 a.u.时,能量至少有11位有效数字的精度;γ=1000 a.u.时,有9位有效数字的精度.对原子高激发态,我们计算了实验室磁场下(磁场为4.7特斯拉)氢原子里德堡态(主量子数n=23)的抗磁谱,得到了至少10位有效数字精度的能谱.本文方法既适用于超强磁场下低能态的计算,同样适合原子高里德堡态抗磁谱的计算,为精确计算强磁场下原子能谱提供了一个新的可行方案.此外,讨论了本文方法推广到平行及交叉电磁场下原子能谱计算的可行性.     

氢离子与里德堡态锂原子碰撞中的电荷转移过程

利用双中心原子轨道强耦合方法研究了H+离子与里德堡态的Li(5d)原子碰撞的电荷转移过程,计算了5d电子转移到氢原子各个次壳层的态选择截面及总截面.研究了态选择截面随俘获电子主量子数及角量子数变化的规律,并尝试给出了解析的标度关系;探讨了标度规律随入射粒子能量的变化,分析了高激发态电子电荷转移过程的动力学机制.     

氢离子与里德堡态锂原子碰撞中的电荷转移过程

利用双中心原子轨道强耦合方法研究了H^＋离子与里德堡态的Li（5d）原子碰撞的电荷转移过程，计算了5d电子转移到氢原子各个次壳层的态选择截面及总截面．研究了态选择截面随俘获电子主量子数及角量子数变化的规律，并尝试给出了解析的标度关系；探讨了标度规律随入射粒子能量的变化，分析了高激发态电子电荷转移过程的动力学机制．     

Fractal dynamics in the ionization of helium Rydberg atoms

We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory.By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization,we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons,and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy.We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons.Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field,and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms.It is shown that,besides the electric and magnetic fields,core scattering is a primary factor in the fractal dynamics.     

Absorption and Recurrence Spectra of Sodium Rydberg Atom in a Strong External Magnetic Field

Using core-scattered closed-orbit theory, we calculate the photoabsorption and the scaled recurrence spectra of sodium Rydberg atom in strong magnetic field below ionization threshold. The non-Coulombic nature of the ionic core have been modified by a model potential, which includes an attractive Coulomb potential and a short-ranged core potential. A family of core-scattered nonhydrogenic closed orbits have also been discovered. The Fourier transformed spectra of sodium atom have allowed direct comparison between peaks in such plot and the scaled action values of closed orbits. The new peaks in the recurrence spectra of sodium atom have been considered as effects caused by the core scattering of returning waves at the ionic core. The results are compared with those of hydrogen case, which show that the core-scattered effects play an important role in alkali-metal atoms.     

Semiclassical Calculation of Recurrence Spectra of He Rydberg Atom in Strong External Fields

Using core-scattered closed-orbit theory and region-splitting iterative method, we calculated the scaled recurrence spectra of helium atom in parallel electric and magnetic fields. Closed orbits in the corresponding classical system have also been obtained. When we search the closed orbits, in order to remove the Coulomb singularity of the classical Hamiltonian motion equations, we implement the Kustaanheimo-Stiefel transformation, which transforms the system from a three-dimensional to a four-dimensional one. The Fourier transformed spectrum of helium atom has allowed direct comparison between peaks in such plot and the scaled action values of closed orbits. The results are compared with those of the hydrogen case, which shows that the core-scattered effects play an important role in the recurrence spectra of the multi-electron Rydberg atom.     

Analysis of the fractal intrinsic quality in the ionization of Rydberg helium and lithium atoms

We study the fractal rhythm in the ionization of Rydberg helium and lithium atoms in an electric field by using the semiclassical method. The fractal structures present a nested relationship layer by layer in the initial launch angles of the ionized electrons versus the escape time, which is defined as the rhythm attractor, and exhibit similar rhythm endings. The gradually enhanced chaotic regions of the escape time plots tend to broaden as the scaled energy increases. In addition,the fractal rhythm changes synchronously with the oscillations of the kinetic energy spectrum. We note that the intrinsic quality of the fractal rhythm is closely related to the kinetic energy distribution, that is, the inherent dynamic properties of the Hamiltonian equations have an impact on the fractal regularities. In addition, different ionizing closed trajectories exhibit iterate properties and the inherent beauty of symmetry. Our results and analysis can not only reveal new laws in the ionization of Rydberg atoms, but also promote the establishment of the dynamic mechanism of fractals.     

Semiclassical calculation of ionization rate for Rydberg hydrogen atoms near a metal surface

The ionization of Rydberg hydrogen atoms near a metal surface at different scaled energies above the classical saddle point energy has been discussed by using the semiclassical method. The results show that the atoms ionize by emitting a train of electron pulses. In order to reveal the chaotic and escape dynamical properties of this system in detail, the sensitive dependence of the ionization rate upon the scaled energy is discussed. As the scaled energy is close to the saddle point energy, the ionization process of the hydrogen atom is nearly the same as the case of hydrogen atom in an electric field. There is only a single pulse of electrons, with an exponentially decaying tail. With the increase of the scaled energy, the ionization rates are similar to the case of the hydrogen atom in parallel electric and magnetic field, a series of electron pulses appear in the ionization process. This is caused by classical chaos, which occurs for the metal surface. Our studies also suggest that the metal surface can play the role of both the electric and the magnetic fields. Our theoretical analysis will be useful for guiding experimental studies of the ionization of atoms near the metal surface.     

Photoionization microscopy of hydrogen atom near a metal surface

We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterns of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom-surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy, the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields.     

Absorption and Recurrence Spectra of Li Rydberg Atom in Perpendicular Electric and Magnetic Fields

We develop the semi-closed orbit theory from two degrees of freedom to three non-separable degrees of freedom and put forward a new model potential for the Li Rydberg atom, which reduces the study of the system to an effective one-particle problem. Using this model potential and the closed orbit theory for three degrees of freedom, we calculate the recurrence spectra of Li Rydberg atom in perpendicular electric and magnetic fields. The closed orbits in the corresponding classical system have also been obtained. The Fourier transformed spectra of Li atom have allowed direct comparison between the resonance peaks and the scaled action values of closed orbits, whereas the nonhydrogenic resonance can be explained in terms of the new orbits created by the core scattering. Our result is in good agreement with the quantum spectra, which suggests that our calculation is correct.     

Semiclassical calculation of the recurrence spectra of He Rydberg atom in perpendicular electric and magnetic fields

Closed orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. By developing the closed orbit theory from two degrees of freedom to three non-separable degrees of freedom, we calculated the recurrence spectra of He Rydberg atom in perpendicular electric and magnetic fields. The closed orbits in the corresponding classical system have also been obtained. Fourier transformed spectra of He atoms have allowed direct comparison between the resonance peaks and the scaled action values of closed orbits, whereas the nonhydrogenic resonance can be explained in terms of the new orbits created by the core scattering. The semiclassical result is in good agreement with the quantum spectra, which suggests that our method is correct.     

Recurrence spectra and dynamical simulation of Rydberg hydrogen atom near a metal surface

By using the closed-orbit theory including the effect of Coulomb scattering together with an electrical image potential approach, the recurrence spectra and the dynamical behaviours of the Rydberg hydrogen atom near a metal surface are presented. Theoretical analysis and numerical simulation reveal that the impacts of the image potential contributing to the recurrence spectrum are qualitatively analogous to that of the parallel electrical and magnetic fields on the Rydberg atom. The recurrence spectra are computed for a few selected scaled energies and the results demonstrate that the scaled energy dominates the dynamical properties of system. With the increase of the scaled energy e from small to large, the whole trend of spectral structure is from simple to complex,and then simple.