【作者】 刘春华；

【导师】 张庆刚； 孟庆田；

【作者基本信息】 山东师范大学 ， 原子与分子物理， 2006， 硕士

【摘要】 强激光场下分子的光电离和光解离已引起人们的多年的关注。相对于弱场来说,强激光场下原子和分子的动力学行为表现出许多新的特征。含时波包方法作为物理化学重要分支,在研究分子反应散射时已经被证明是一种非常有效的方法,其理论框架在分子物理和场与物质相互作用等研究领域也有着广泛的应用。含时波包法有许多优点,除了数值计算上的高效率外,该方法还为动力学提供了物理意义明确而直观的图像,它既具有经典的直观,又不乏量子力学的准确。另外,含时量子波包法尤其适用于研究体系随时间演化的问题。目前对强场下分子的光电离动力学行为的理论研究主要集中在一些小分子上。对小分子的动力学理论处理中,一维两态问题是最简单的情况。对强场下小分子多光子电离的处理不仅对处理大分子的强场效应有借鉴作用,对理解和实施原子与分子过程的激光操控也具有重要的理论和实践意义。共振增强多光子电离光电子能谱(REMPI PES)技术是研究小分子激发态的有效手段。本论文利用量子力学含时波包传播中的分裂算符-傅立叶变换方法研究强场下双原子分子RbI的1+3多光子电离时间分辨光电子能谱。主要进行了以下几个方面的工作:(1)首先给出了RbI分子1+3多光子电离的理论模型,并写出模拟过程的含时Schr?dinger方程。由于电离过程涉及到两个离子态,模拟过程同时考虑了三光子电离过程和自电离过程。(2)利用分裂算符-傅立叶变换方法演化波包,模拟得到了不同探测—延迟时间下RbI分子1+3多光子电离的光电子能谱。由于模拟过程同时考虑了两个电离过程,所得光电子能谱由两部分信号组成。(3)通过对时间分辨光电子能谱进行分析,得到了强场对RbI分子势能面施加影响的信息。结果表明,泵浦-探测延迟时间对光电子能谱的强度和位置均有影响,而这种影响实质上是由于强场的存在改变了相关势能面的位置以及存在势能面之间的交叉所导致的。所得结论不仅有助于理解强场下分子的动力学行为,而更多还原

【Abstract】 The photoionization and photodissociation of molecules in strong laser field haveattracted much interest in recent years. When an atom or molecule is subjected to anintense external field, some new phenomena will appear. The wave packet dynamics is animportant branch of physical chemistry. In the molecular collision study, it has beenproved to be very effective. Its theoretical framework has many applications in molecularphysics and the field-matter interaction systems. The time-dependent wave-packet methodis very attractive. Besides the numerical efficiency, time-dependent wave-packet methodis conceptually simple. It provides a classical-like interpretation and also the quantumprecision. And besides, the wave-packet method is very applicable in dealing with theevolution of the system.Recently, in the theoretical research fields of photoionization dynamical behavior,much attention is focused on small molecules. In the theoretical treatment of singlemolecule dynamics, one spatial dimension and two-state system is the simplest one. Theintroduction of the appropriate computational approaches to the dynamics ofwave-packets on this system is very important for understanding the treatment of complexsystems. Besides, it has theoretical and practical instruction for chemical reactioncontrolling.Resonance Enhanced Multi-photon Ionization Photoelectron Spectroscopy (REMPIPES) is an excellent method in the studies of the excited states of small molecules. In thisthesis, we study the multi-photon ionization time-resolved photoelectron spectroscopy ofRbI molecule in strong laser field. The “split operator-Fourier transform” method ofquantum mechanics time-dependent wave packet propagation is employed in thesimulation process. The main work is given as below.(1) Firstly, we introduce the theoretical model of the 1+3 multi-photon of RbImolecule, and give the time-dependent Schr?dinger equation of the simulation process.Because two ion states are involved in this ionization process, both the normalthree-photon ionization process and auto-ionization process are considered in thesimulation.(2) The wave-packet is propagated using the “split operator-Fourier transform”method. The time-resolved photoelectron spectrum of RbI molecule 1+3 multi-photonionization is simulated using the time-dependent wave-packet method. Because twoionization process are involved in the simulation, the photoelectron spectrum is composedof two signals.(3) The effect of laser fields on the RbI interaction potentials is obtained throughanalyzing the time-resolved photoelectron spectrum. The calculated results show that thechange of delay time will influence both the position and the intensity of thephotoelectron spectrum. This influence is substantially due to the existence of the crossingbetween excited states and the strong laser field which will change the position of relevantcurves. The change of delay time may influence the ionization ratio to some extent, andthe idea may be instructive for chemical reaction controlling.This submitted work is divided into five chapters. The first chapter is theintroduction, which briefly discusses the basic theory of molecular reaction dynamics.Also presented is the development of the time-dependent wave-packet method. Chaptertwo introduces the resonance-enhanced multi-photon ionization photoelectronspectroscopy technique and the photoelectron spectrum conception. In chapter three, thetheoretic and computational methods used in the simulation process are presented. Inchapter four, the theoretical model of RbI 1+3 multi-photon ionization is given. The“split operator-Fourier transform” method of time-dependent wave packet propagationis employed to reproduce the experimental obtained MPI PES of RbI molecular indifferent pump-probe delay time. The simulated photoelectron spectra fairly wellreproduced the experimental result. The effect of laser fields on the RbI interactionpotentials is obtained through analyzing the time-resolved photoelectron spectrum. Thelast chapter is our conclusion.更多还原