Time-dependent Study Of Multi-photon Ionization For NaK Molecules In A Double-well Potential

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. The wave packet dynamics is an effective method used for studying the excitation and ionization dynamics of molecules in the femtosecond 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 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.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 NaK molecule in a double-well potential. 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. To present conveniently the influence of field-matter interaction, the rotating wave approximation is introduced, and the laser-induced transition is reduced to potential crossings. This rather general theory of wave-packet dynamics is related to femto-time molecular physics and chemistry.(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 NaK molecule 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. The wave packet distribution of the 6 1Σ+ stste can be controlled by altering the parameters of the laser pulses. And it is possible to monitor the splitting of the wave packet at the potential barrier. In addition, we can obtain the wave packet dynamic information of the 6 1Σ+ state from the photoelectron energy spectra.This submitted work is divided into five 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 NaK 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 NaK molecular in different pump-probe delay time.