| The photoionization and photodissociation of molecules in strong laser field have attracted much interest in recent years. When an atom or molecule is subjected to an intense external field, some new phenomena will appear. As an effective method, the wave packet dynamics has been used for studying the excitation and ionization dynamics of molecules in the pulsed laser field. Besides the numerical efficiency, this method is conceptually simple. It provides a classical-like interpretation and also the quantum precision. And besides, the wave-packet method is very applicable in dealing with the evolution of the system.Recently, in the theoretical research fields of photoionization dynamical behavior, much attention has been focused on small molecules. 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.Resonance Enhanced Multi-photon Ionization Photoelectron Spectroscopy (REMPI PES) is an excellent method in the studies of the excited states of small molecules. In this thesis, we study the multi-photon ionization time-resolved photoelectron spectroscopy of ClO radical in strong laser field. The"split operator-Fourier transform"method of quantum mechanics time-dependent wave packet propagation is employed in the simulation process. The main work is given as follows.(1) The fundamental theory of wave-packet dynamics associated with 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.(2) The basic theory of the excited-state molecular photo-ionization dynamics is presented. A survey of work using resonance-enhanced multi-photon ionization and double-resonance to study excited-state photo-ionization dynamics in molecules is reviewed . The theoretical method to deal with the transition moment is briefly given in the theoretical background. This treatment of photo-ionization processes can be used as a basis for understanding excited-state photo-ionization. As a major investigation object through out our work, the technique of MPI TRPES is introduced. Its characteristics, its differences with the ion-current spectrum of multiphoton ionization, as well as its application to molecular dynamics are also discussed.(3) The wave-packet is propagated using the"split operator-Fourier transform"method. The time-resolved photoelectron spectrum of ClO radical 2+1 multi-photon ionization is simulated using the time-dependent wave-packet method. The calculated results show that the change of delay time and photo energy will influence the photoelectron spectrum.This submitted work is divided into four chapters. The first chapter is the introduction, which briefly discusses the development of molecular reaction dynamics and the time-dependent wave-packet method. Chapter two introduces the basic theories of wave-packet method. Chapter three introduces the resonance-enhanced multi-photon ionization photoelectron spectroscopy technique and the photoelectron spectrum conception.In chapter four, the theoretical model of ClO 2+1 multi-photon ionization is given. The"split operator-Fourier transform"method of time-dependent wave packet propagation is employed to reproduce the experimental obtained MPI PES of ClO radical in different pump-probe delay time.
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