【作者】 王文鹏；

【导师】 林圣路；

【作者基本信息】 山东师范大学 ， 原子与分子物理， 2008， 硕士

【摘要】 近年来,高里德堡原子在强外场中的光吸收现象引起人们广泛的关注,它是研究和发展量子混沌概念的一个典型实例。半经典闭合轨道理论由于具有物理图像清晰、应用范围广泛等特点,被普遍用来解释此类现象,并成为实现联结经典理论和量子理论的重要桥梁。该理论很好地解释了氢负离子在各种外场下的光吸收问题以及氢原子和其他类氢原子和分子在电磁场中的光激发、电子波包动力学、微腔输运以及环境中激发态原子的寿命等问题。与氢原子相比,对多电子原子(如氦原子,锂原子等),理论处理要困难得多,由于离子实散射的作用,其相应的经典行为是混沌的。通过对多电子原子强场行为的实验与理论研究,人们发现必须考虑离子实的作用,实散射产生了在单电子中没有的组合轨道,使轨道数目迅速增加。闭合轨道理论不再适用,因而必须对理论本身做适当的改进和推广。本文在扩展的有限分辨率的闭合轨道理论框架内,采用了包括离子实散射的分区自洽迭代方法,结合B.Hüpper的模型势和量子亏损理论,引进适当的模型势,计算了谱的大标度结构(ΔE大,相应时间ΔT小),即作用量较小的闭合轨道的贡献,因为它们对谱性质起决定性作用。我们得到了B = 3.5T,F =18.84V cm情况下,标度能量ε= ? 0.03,主量子数n≈40, M =1三重态He原子和Li原子在平行电磁场回归谱,从中可以看到,短程核势以及离心势作用于闭合轨道和波函数,因而必将对回归谱产生重要影响。与氢原子结果做了比较,进一步证实了上述结论。为讨论关于磁量子数对谱的影响,我们还研究了在标度能量ε= ? 0.03和标度电场f = 0.01的情况下, M =0三重态He原子和Li原子在平行电磁场中的闭合轨道和光吸收的回归谱。通过经典轨道和回归谱的比较,可以更深入的理解M =1体系不同于M =0体系的动力学特点,得出M = 1情况中离心势会减弱离子实短程衍射效应和电子的关联,并且将显著改变光吸收的回归谱。对于M =1多电子里德堡原子这一研究领域,我们的工作既是对半经典理论的推广,又是对该理论的验证和完善。由于现在还没有M =1三重态He原子和Li原子在平行电磁场中的回归谱的实验结果的比较,希望理论计算能对未来的实验工作有一定的参考作用。论文共分为六章。第一章为综述,简要回顾半经典闭合轨道理论的要点及其发展。第二章介绍了模型势和标度变换回归谱学,给出了包括离子实势的多电子原子的模型势,还给出了在平行电磁场中的标度变换。第三章详细描述闭合轨道理论的物理图像和理论推导。第四章计算了平行电磁场中Li ( M =0, M =1)里德堡原子的回归谱,并与H里德堡原子的谱相比较,着重分析核散射和短程模型势效应。第五章给出了He( M =0, M =1)里德堡原子的回归谱,比较分析了两种不同磁量子数下的谱,讨论轴对称的排斥势的影响。第六章是全文的总结,并对可能的发展和应用作补充说明。更多还原

【Abstract】 The photo-absorption phenomenon of highly excited Rydberg atoms in strong external fields has attracted much attention in recent years, which is a typical example for understanding the conception of quantum chaos. The semiclassical closed-orbit theory has been extensively used to explain this phenomenon due to its enlightened physical picture and wide availability such that has become a bridge between quantum and classical theory. This theory has successfully calculated and interpreted the photo-absorption spectra of H ? and has been applied to describe the recurrence spectra of photo-excitation, wave packet dynamics of some atoms and molecules such as H , Li atoms, H 2, NO molecules and so on. Corresponding extended methods have applied to study the transport properties of micro-cavity and the investigation on the atoms life in environment.Other than the hydrogen atom, a theoretically studying of the multielectron atom is more difficult. The multielectron atoms are quantum atomic systems whose underlying classical dynamics is chaotic induced by ionic core scattering. Previously theoretical and experimental studies have found that the effects of the non-hydrogenic ionic core should be considered. It is core scattering that leads to new recurrence peaks called combination recurrence. Therefore, it is necessary to correct and extend the primitive standard closed-orbit theory to include this affect.In this paper, by using special regions-splitting consistent and iterative method combined together with the quantum defect theory and model potential approach, we calculate the closed orbits and the recurrence spectra in frame of extended closed-orbit theory with finite resolution. The spectral structure is measured in larger energy scale (or equivalent to a shorter time scale). That is to say, we only consider the contributions of closed orbits with smaller actions that are the most decisive for the spectral structure. We obtained the recurrence spectra of triplet helium and lithium atoms with n≈40 and M =1 in parallel electric and magnetic fields at scaled energyε= ?0 .03. The results reveal that the core-scattering effects are important, particularly, the short-range model combining with the repulsive potential have remarkably changed both the closed orbits and wave function of the electrons, thus altered obviously the yielded recurrence spectra, which can be readily conformed by comparison with the recurrence spectra of H atoms at the same condition.In order to discuss the effects of magnetic quantum number on the recurrence spectra, we calculate the recurrence spectra of M =0 He and Li atoms in the parallel electric and magnetic fields at scaled energyε= ?0 .03 and scaled electric field f = 0.01. Comparing the two cases, we find that the dynamical feature of M =1 is different from M =0. The centrifugal barrier make the diffraction arising from ionic core and the correlation of electrons weaken, which plays a great role in the recurrence spectra.For the studies of multielectron Rydberg atoms, our works are not only the extension but also the validation and supplement for the closed-orbit theory. So far, there has been no experiments of M =1 He and Li atoms in the parallel electric and magnetic fields that compared to the recurrence spectra in theory, we expect that our calculations may help to design new experiment in future.This thesis consists of six chapters. The first chapter is summarization, which briefly introduces the development history of semiclassical closed-orbit theory. The second chapter is devoted to the model potential and the scaled variable recurrence spectroscopy. We give the proper model potential of multielectron atoms and the scaled variable in parallel external electric and magnetic fields. The third chapter describes the closed orbit theory for multielectron Rydberg atoms. The fourth chapter presents the calculating results of the recurrence spectra of Li ( M =0, M =1) Rydberg atoms in parallel electric and magnetic fields and compares our results to the hydrogen situation. Our emphasis is to analyze the effects of the model and short-range repulsive potentials. The fifth chapter presents the calculating results of the recurrence spectra of He ( M =0, M =1) Rydberg atoms in parallel electric and magnetic fields. By comparison between two different magnetic quantum numbers, the effects of the short-range repulsive potential with cylindrical symmetry have been analyzed in detail. The sixth chapter is the conclusion of this work and expectation.更多还原