The Investigation Of The Photoassociation Dynamics Of Alkali Dimers

Molecular reaction dynamics is the basic field of the chemical physics research. It introducesthe modern physical and chemical analysis methods and studies the microcosmic dynamics andprinciple of the chemical reaction on the atomic and molecular level. It can elucidate not onlystructures, characters and functions of all kinds of transient species during reactions, but alsointrinsic law of chemical reaction from the research on state-to-state reaction dynamics and theinteraction of coherent states. The wave packet dynamics is an important branch of physicalchemistry. As an effective method, the time-dependent wave-packet method has been used forstudying the vibrational excitation and ionization dynamics of molecules in the strong pulsedlaser field. Its theoretical framework has many applications in molecular physics and thefield-matter interaction systems. Besides its numerical efficiency, time-dependent wave-packetmethod is also conceptually simple. It provides a classical-like interpretation with the quantumprecision. Besides, the time-dependent wave-packet method is especially applicable in dealingwith the system which evolves with time.In recent years, with the development of the ultrashort pulse laser techniques, many newphenomena of laser-molecule interaction have been observed and investigated, such as AC-Starkshift, multiphoton ionization, laser-induced continuum structure and photoassociation reaction.As a reversed process of photodissociation, photoassociation has been studied bothexperimentally and theoretically. Alkali dimers are indeed chosen systems for the investigation tothe photoassociation of ultracold molecules due to their large permanent dipole moment in thelowest vibrational level of their ground state. However, the observation and control ofphotoassociation dynamics by using short pulse techniques，as the extension of femtochemistry tobinary reactions，are still at its infancy and remain a challenge. In the present paper we take NaCsand NaRb molecule as examples to investigate the photoassociation dynamics of the alkali dimersin the ultra-fast laser fields. Quantum wave packet method used for solving the time-dependentSchr dinger equation is implemented for revealing the reactive dynamics process.First, we theoretically investigate the two step association process of NaCs molecule. Theeffect of the laser parameters on the vibrational state-selectivity is discussed in detail. Meanwhile, the impact of the laser pulse intensity and laser frequency are analyzed particularly.Second, the photoassociation process with photodissociation is simulated. The NaCsmolecules just in lower vibrational levels can be obtained through the effect of the dissociationprocess.Third, we investigate the photoassociation dynamics of cold NaRb moleculars controlled byan asymmetric laser pulse called slowly-turned-on and rapidly-turned-off (STRT) laser pulse. Thepopulation distribution changing with the laser falling time and the delaytime is mainly discussed.This submitted work is divided into four chapters. The first chapter is the introduction, whichbriefly introduces the development of molecular reaction dynamics and the basic theory of highorder harmonic generation. Chapter two presents the basic theory and method of wave-packetdynamics. Chapter three introduces the wave packet dynamics simulation of the photoassociationprocess. In chapter four, we calculate the population distribution varies according to the laserparameters.