Time-dependent Wave-packet Approach To The Photondissociation Of Diatomic Molecules

Molecular reaction dynamics studies the microcosmic dynamics and principle of the chemical reaction based 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. Photodissociation is at the heart of photochemistry, and it is also an important embranchment in molecular reaction dynamics.The time-denpendet wave-packet dynamics as the tool of molecular reaction dynamics research has many applications in molecular physics and the field-matter interaction systems. The time-dependent wave-packet method is very attractive. Besides the numerical efficiency, time-dependent wave-packet method is conceptually simple. It provides not only a classical-like interpretation,but also the quantum precision.This thesis studies the absorption cross section of diatomic molecule-NaH molecule during its photodissociation process on the basis of the Born-Oppenheimer approximation theory. The influence of the different propagation methods, the different potential energe curves, as well as the different initial wave-packets to the absorption cross section is discussed. The main contents and results are presented as follows.First, this thesis calculates the absorption cross section of NaH molecule from ground state X 1∑+( v" = 0) to B 1∏using Fourier grid Hamiltonian method to solve the time-dependent Schr?dinger equation and using split operator method as a wave-packet propagation scheme on the basis of the adiabatic approximation theory. In order to study the effects of different wave-packet propagation scheme on photodissociation cross section of NaH, The results obtained by plit-operator method was compared with those obtained by the Chebyshev propagation scheme. The results indicate that the two schemes are equivalent in calculate the total absorption cross section. Then, according to the experimental result of the threshold energe, the potential energe curves were rearranged, the results we obtained were compaired with the rusults gived by Bhattacharjee et al. , the key influence factor of photodissociation cross section was obtained. Last, Four different vibrational states ( v " = 0,1,2,3)were taken as initial wave-packets to investagate the influence to the photodissociation cross section.This submitted work is divided into five chapters. The first chapter is the introduction, which briefly discusses the basic theory of molecular reaction dynamics. Also presented is the development of the time-dependent wave-packet method. Chapter two introducts the development and significance of photodissociation dynamics. In chapter three, the theoretical and computational methods used in photodissociation dynamics are presented. The research process and the results are given particularly and the influence of different propagation methods,the different potential energe curves,the different initial wave-packets on the photodissociation cross section are disscussed in the fourth chapter. The summary and the prospect are represented in the last chapter.