Influence Of Laser Fields On The Vibrational Excitation Of Molecules And Its Wave-packet Dynamical Investigation

Molecular reaction dynamics is the basic field of the chemical physics research. It introduces the modern physical and chemical analysis methods and studies the microcosmic dynamics and principle of the chemical reaction on atomic and molecular level. It can elucidate not only structures, characters and functions of all kinds of transient species during reaction, but also intrinsic law of chemical reaction from the research on state-to-state reaction dynamics and the interaction of coherent states. The wave packet dynamics is an important branch of physical chemistry. As an effective method, the time-dependent wave-packet method has been used for studying the vibrational excitation and ionization dynamics of molecules in the strong pulsed laser field. Its theoretical framework has many applications in molecular physics and the field-matter interaction systems. Besides its numerical efficiency, time-dependent wave-packet method is conceptually simple. It provides not only a classical-like interpretation, but also the quantum precision. And besides, the time-dependent wave-packet method is especially applicable in dealing with the system which evolves with time.Recently, interaction of intense laser pulses with atomic and molecular systems has been a subject of a number of theoretical and experimental studies during the past years. From the experimental phenomenology, an adequate description of atomic or molecular processes in intense fields involving freedoms of electrons and nuclear is required. In general, the evolution of a wave packet on the corresponding potential energy surface can be employed to described the molecular dynamics process. In the theoretical research fields of photoionization dynamical behavior, much attention is focused on small molecules. In the theoretical treatment of single molecule dynamics, one spatial dimension and two-state system is the simplest one. The introduction of the appropriate computational approaches to the dynamics of wave-packets on this system is very important for understanding the treatment of complex systems. Besides, it has theoretical and practical instruction for chemical reaction controlling. The treatment about small molecules'multi-photon ionization not only use for reference about the big molecules'action in intense external field, but also have theoretical and practical significance to understand or carry the laser control on atom and molecule.In this paper the vibrational population of NO and ClO radical in the intense laser fields was studied by the split-operator technique of time-dependent wave-packet method in quantum mechanics. The main work is given as follows:(1) The fundamental theory of wave-packet dynamics associated in our work is introduced. This starts by giving the basic concept of wave-packet and its application to dynamics. Then take the diatomic molecule as an example, how the time-dependent Schr?dinger equation with the proper Hamiltonian is solved for the system is shown. The numerical tools used for solving the wave-packet dynamics from a coupled Schr?dinger equation are also provided. This rather general theory of wave-packet dynamics is related to fs-time molecular physics and chemistry.(2) We have solved the time-dependent Schr?dinger equation by using Fourier grid Hamiltonian method, and obtained the eigenfunction of diatomic molecules for the different ground vibrational state. The wave-packet is propagated using the"split operator-Fourier transform"method. Because the potential operator in the coordinate representation is diagonalizable, and the kinetic energy operator in the momentum representation is diagonalizable, in the calculation process, we use Fourier transform method to achieve transformation of coordinate space and momentum space for achieving the role of the Hamiltonian operator on the wave function.(3) Taking NO and ClO radical in intense laser fields as examples, we investigate the influence of laser parameters on vibrational population. The results showed that the vibrational states closest to the resonance region can acquire the most probable distribution. The resonance region can be changed by changing the laser parameters, thereby, the vibrational population changes. The vibrational distribution in the different electronic states changes with the delay time of the two intense laser pulses. As for the influence of pulse delay time, it can be ascribed to the effect of the coupling between two pulses. The conclusions not only help to understand molecular dynamics in the strong field, but may be instructive for chemical reaction controlling.This submitted work is divided into four chapters. The first chapter is the introduction, which briefly discusses the basic theory of molecular reaction dynamics. Also the development of the wave-packet dynamics is presented. Chapter two introduces the major theory of wave-packet dynamics. Chapter three introduces diatomic molecules wave packet dynamics simulation under intense laser field. In chapter four, the vibrational population of NO and ClO radical in different electronic states is given. The"split operator-Fourier transform"method of time-dependent wave packet propagation is employed to reproduce the experimental obtained the vibrational population in different laser parameters and different pump-probe delay time.