Ionization And Dissociation Dynamics Of Diatomic Molecules In Strong Femtosecond Laser Field

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 Chapterâ…¢through V.First of all,the molecular reaction dynamics and the femtosecond science technology are introduced in chapterâ… .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.Chapterâ…¡presents 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 Chapterâ…¢,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.Chapterâ…£is 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 Chapterâ…¤,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.