【作者】 苗向阳；

【导师】 宋鹤山； 韩克利；

【作者基本信息】 大连理工大学 ， 理论物理， 2009， 博士

【摘要】 在分子科学中,强激光场条件下研究分子动力学是一个具有挑战性的热点课题。在强激光场条件下探索物质的新特性以及以强激光场作为工具来研究怎样操作和控制物质等方面,该研究方向都有非常重大的应用前景。面对强场实验中层出不穷的新现象,从理论上探索这些实验现象背后的规律,建立合理的理论模型来解释这些实验现象就显得非常重要了。鉴于含时量子力学方法的高效性、直观性以及准确性,它被广泛的应用于分子动力学的理论研究当中。本论文采用含时量子力学方法针对不同分子体系在飞秒强激光场条件下的电离解离现象进行了模拟计算,得到了与实验符合较好的计算结果,并且从理论上很好的解释了实验现象。论文共包括五章,其中我们的主要工作是第三章到第五章。第一章简单介绍了分子反应动力学以及飞秒科学技术,回顾了近些年来飞秒激光的发展,简单阐述了飞秒激光强场中的电离解离现象以及量子含时波包方法,最后给出了本论文的主要工作内容。第二章首先介绍了波包和势能面的基本概念,然后阐述了耦合能级的基本理论,最后详细的介绍了含时量子波包计算方法。其中主要包括初始波包的计算、快速傅里叶变换方法以及常用的时间传播方法。第三章我们对I₂^-离子的光电离过程进行了理论研究。针对I₂^-离子飞秒时间分辨的光电离实验的结果,建立了一维含时波包模型,并且从理论上模拟了I₂^-离子的光电子能谱。和前人采用半经典的方法对该实验结果进行模拟相比,我们在这里采用了精确的量子力学方法来处理整个电离过程。我们的计算结果和实验结果符合的相当好,并且合理的解释了I₂^-离子整个光电离实验过程中的现象。第四章分为两部分。在第一部分中我们首先对NaI分子的光电离过程进行了理论研究。鉴于前人理论计算结果与实验结果的明显差异,我们采用了精确的量子力学方法对整个实验过程进行了理论模拟,理论结果和实验结果符合的很好。除此之外,我们还对整个光电离过程进行了合理的理论解释。在第二部分中我们从理论上对NaI分子的光解离过程进行了研究。在NaI分子的光电离过程中伴随有解离过程,并且这两个过程是相互竞争的。在不同的激光场条件下,电离和解离的产率都不相同。这点对于相关方面的实验工作来说,具有比较重要的指导意义。第五章我们通过计算得到了Na₂分子在强激光场条件下的光电子能谱。我们观察到了波包在中性激发态势能曲线上的周期性振动,而且还对各种电离机制进行了合理的分析。在整个光电离过程中,我们可以看到在不同的延迟时间条件下会有不同性质的光电离发生。通过计算结果我们还发现,通过控制延迟时间的长短我们可以控制自由电子动能的大小。更多还原

【Abstract】 In molecular science,molecular dynamics study in strong laser fields is a challenging and hot topic.This research area has very significant application prospects in respects of exploring the new features of materials in strong laser fields as well as studying how to operate and control the substances with the intense laser fields as a tool.In the face of new phenomena detected in strong field experiments,it is very important to explore the law behind these experimental phenomena and set up a reasonable theoretical model to explain the phenomena of these experiments.Due to the efficiency,the intuition,and the accuracy of it,the time-dependent quantum mechanics method has been widely used in the theoretical study of molecular dynamics.In this dissertation,the simulations of the phenomena of ionization and dissociation in Femtosecond laser fields have been done by using the time-dependent quantum mechanics method in different molecular systems.These simulations accord well with the experimental results,and the experimental phenomena have been well explained.The dissertation contains five chapters,with our contributions given in ChapterⅢthrough V.First of all,the molecular reaction dynamics and the femtosecond science technology are introduced in chapterⅠ.Secondly,the development of femtosecond laser in recent years is reviewed.Thirdly,the ionization and dissociation phenomena in femtoscond laser field as well as the quantum time-dependent wave packet method are briefly described.The main work of the dissertation is given at the end of this section.ChapterⅡpresents firstly the basic concepts of wave packets and potential energy surfaces. Then,the basic theory of energy coupling is introduced.Finally,the quantum timedependent wave packet method is explained in details,which includes mainly the calculation of the initial wave packet,the fast Fourier transform method,and the time-transmission method commonly used.In ChapterⅢ,the theoretical study of photoionization process about I₂^- ion is performed. According to the experimental results,a one-dimensional time-dependent wave packet model is set up when the photoelectron spectroscopy is simulated.Compared with the earlier simulations using the semi-classical method,the accurate quantum mechanics method is adopted here to deal with the entire ionization process.The theoretical results accord well with the experimental ones and the experimental phenomena of photoionization process are illuminated reasonably.ChapterⅣis divided into two parts.In the first part,theoretical research is performed on the photoionization process of Nal molecule.In view of significant differences between previous theoretical calculations and experimental results,the accurate quantum mechanics method is adopted in the theoretical simulation,and the theoretical results are consistent with the experimental ones.In addition,a reasonable theory is used to explain the photoionization process.In the second part,theoretical research on the dissociation process of NaI molecule is carried out.Photoionization process of NaI molecule always occurs accompanying dissociation process and these two processes are competing.Ionization and dissociation results change with the laser field.This point has important guiding significance for the relevant experimental work.In ChapterⅤ,the photoelectron spectrum of Na₂ molecule in strong laser field is calculated. It is observed that the periodic vibration of the wave packet on the potential energy curve of the neutral excited state and the reasonable analysis of different ionization mechanisms is obtained.In the whole process of photoionization,it can be seen that different photoionization occurs in different delay time.From the results of calculation,it is found that the level of free-electron kinetic energy can be controlled by adjusting the length of the delay time.更多还原