The Investigation Of The Photodissociation Dynamics Of Diatomic Alkali Molecule

Photodissociation dynamics, as an important branch of molecular reaction dynamics,mainly studies the produced process of the fragments when the molecules are dissociated afterabsorbing photons and the energy and spatial distribution of these fragments. As thesemi-process of molecular collision reactions, photodissociation dynamics can make peoplehave a deeper understanding of the motion between electronic and nuclear, which can provide abasis for obtaining the information of the initial state of the reactants and the final state of theproducts. According to the difference of the dissociation process, generally thephotodissociation reaction is divided into direct-dissociation and predissociation. For diatomicmolecules, predissociation is very important. In that case, there may be an overlap betweendiscrete levels and continuous levels, which can result in the Auger process (i.e. non-radiativetransition). When the Colony law is satisfied, and the electronic transition probability is notabnormally small, one can see the diffusion in the absorption band.The time-dependent wave packet method is one of the most important methods in physicalchemistry. It has been proved to be an effective approach to studying the dissociation dynamics,ionization dynamics and vibrational excitation of molecules in the pulsed laser field. Itstheoretical framework has been widely used in the treatment of molecular physics and thefield-matter interaction systems and so on. The advantages of the time-dependent wave packetmethod are shown not only in the high efficiency of the numerical calculation, but also in theintuitive picture of the dynamics. It provides a classical-like interpretation with the quantumprecision. In addition, the time-dependent quantum wave packet method is particularly suitablefor dealing with the system which evolves with time.In recent years, with the development of the laser techniques, many new phenomena of thelight-matter interaction have been observed and investigated, for example, multiphotonionization, multi-channel dissociation, coherent control of dissociation and photoassociationreaction etc. The photodissociation dynamics, which related to the core problems of elementary chemical reactions, i.e., the breakage and formation of chemical bonds, so the study of thephotodissociation process can help us understand the molecular mechanism of the bondbreaking process, so as to better achieve the control of the field to the chemical reaction. At thesame time, in the two-step photoassociation process, the photodissociation process is veryimportant to the results of the photoassociation reaction. So it is very meaningful for the studyof photodissociation dynamics. In recent years, the alkali metal molecules, especially theheteronuclear cold molecules, have become a research focus, because of their characteristics ofpermanent electric dipole moment and tunable long range of the dipole-dipole interaction.In this paper, we investigate the photodissociation dynamics of the NaCs molecules byusing the time-dependent quantum wave packet method. The effects of the characteristics ofpotential energy surfaces, such as the avoided crossing, the predissociation limit and the laserparameters on the dissociation probability, the absorption spectrum and the kinetic energyspectrum and so forth are discussed in detail. The full text is divided into four parts. The firstpart is the introduction, which mainly introduces the basic theory of molecular reactiondynamics and photodissociation dynamics. In the second part, the basic theory of thetime-dependent wave packet dynamics, together with the method used to calculate the reactionprobabilities, the absorption spectrum and other related theories, is described. The third partintroduces simulated photodissociation dynamics of diatomic alkali molecule in the laser field.And the fourth part is a general summary of the whole thesis and prospects of thephotodissociation dynamics.