Time-dependent Wavepacket Approach To The Photodissociation Cross Section Of Small Molecules

The wave packet dynamics is an important branch of physical chemistry. In the molecular collision study, it has been proved to be very effective. Its theoretical framework 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 a classical-like interpretation and also the quantum precision. So, time-dependent wave packet method is generally used in photodissociation study. Photodissociation is at the heart of photochemistry, and it is also an important embranchment in molecular reaction dynamics. However, people have been paying attention to photoabsorption cross section in the field of the photodissociation theroy.This thesis studies the absorption cross section and the corresponding absorption spectrum of different electronic states for small molecular-IBr molecular during its photodissociation process on the basis of the Born-Oppenheimer approximation theory. We discuss the absorption spectrum on the different propagation methods, investigate the relationship of the absorption spectrum and initial wave-packet. The main contents and results are presented as follows.First, this thesis calculates the absorption cross section which is similar to the experimental outcomes of every electronic state of IBr molecular using the Chebyshev propagation scheme on the basis of the adiabatic approximation theory. Then, in order to study the effects of different wave-packet propagation scheme on photoabsorption cross section of IBr, we use the split operator-Fourier transform propagation scheme to investigate the photoabsorption cross section of C state of IBr and compared with the results which are obtained by Chebyshev propagation scheme. The results indicate that the two schemes are equivalent in calculate the total absorption cross section. Last ,we take three different vibrational states as initial wave-packet to investagate the cross section with the study of C state and received the identical results with classical theory.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 conception of wave-packet and the development of the time-dependent wave-packet method. Chapter two introducts the development and significance of photodissociation dynamics. Also given is the types of photodissociation dynamics. In chapter three, the theoretic and computational methods used in the investigation of photodissociation cross section are presented. The research process and the results are given particularly and the results are disscussed and compared with the experimental outcomes in the fourth chapter. The summary and the prospect are represented in the last chapter.