| 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 pulsed laserfield. Its theoretical framework has many applications in molecular physics and the field-matterinteraction systems. Besides its numerical efficiency, time-dependent wave-packet method isconceptually simple. It provides a classical-like interpretation with the quantum precision.Besides, the time-dependent wave-packet method is especially applicable in dealing with thesystem which evolves with time.With the development of laser technology in recent years, high-precision and high-resultingexperimental techniques in the field of molecular reaction dynamics has been widely used, andgained a lot of very important research findings. It has been an interesting and popular researchtopic in the physics and chemistry to control the electronic and nuclear movement by use of theultrashort laser pulses. Quantum wave packet method based on the Schr dinger equation candescribe the time-dependent dynamic processes of the system detailedly, so it is widely used in thestudy of molecular reaction dynamics. The treatment about diatomic molecular dissociation dynamicsis not only used as a reference in dealing with the interaction between big molecules in intense field,but also has theoretical and practical significance to understand and carry out the laser control onatomic and molecular processes.The time-dependent wave packet theory includes Fourier grid method (FGH) and the splitoperator method, which the former could solve the Schr dinger equation of the initial moment and the later could spread the wave function. We take the hydrogen molecular ion as the object of thestudy and calculate the probability of dissociation and Coulomb explosion in the strong field,then further study the impact of the field intensity, wavelength on the probability of dissociationand Coulomb explosion. It was discovered that the rare gas in a strong laser field can producthigh harmonic generation, and recently so is discovered in the molecular gas. We calculate thehigh harmonic generation during the interaction between the hydrogen molecular ion and laserfields, and study effects of the vibrational quantum number on the high harmonic generation. Themain work is given as follows:(1) The fundamental theory of wave-packet dynamics associated in our work has beenintroduced. This starts by giving the basic concept of wave-packet and its application to dynamics.Then we take the diatomic molecule as an example to show how to solve the time-dependentSchr dinger equation with the proper hamiltonian. The numerical tools used for solving thewave-packet dynamics from a coupled Schr dinger equation are also provided. This rather generaltheory of wave-packet dynamics is related to fs-time molecular physics and chemistry.(2) We have solved the time-dependent Schr dinger equation by using Fourier gridHamiltonian method, and obtained the eigenfunction of diatomic molecules for the differentground vibrational state. The wave-packet is propagated using the“split operator-Fouriertransform”method. So the wave packet propagation can be achieved and the wave function at anymoment can be obtained.(3) We have already calculated the probability of dissociation and Coulomb explosion ofhydrogen molecular ion in the strong field; we have further researched the influence of laserparameters on dissociation probability. We find that the frequency of the laser becomes lower withthe increase of the wavelength, the photon energy reduces with the increase of the wavelength,then it becomes far away from the resonance zone, which lead to the decrease of the number ofhydrogen molecular ion that transit to the dissociative state. The occurrence probability of theCoulomb explosion channels as well as the occurrence probability of the dissociation channel alsodecreases. With the enhancement of the laser intensity, the number of hydrogen molecular ionexcited to the dissociation state from the ground state becomes more, and the numbers of hydrogenmolecular ion without any dissociation decrease, the occurrence probability of the hydrogenmolecular ion Coulomb explosion channels as well as the occurrence probability of the dissociation channel increases. The conclusions not only help to understand molecular dynamicsin the strong field, but may be instructive for chemical reaction controlling.(4) We have calculated the high order harmonic generation spectrum in the femtosecondlaser field. The investigations indicate that the high order harmonic generation spectrum in thestrong laser field basically has the structure of falling-plateau-cutoff. The intensity of the highorder harmonic generation in platform area becomes stronger with the increase of the vibrationalquantum number. The reason of which is that with the increasing of vibrational quantum number,the ionization potential of the system decreases gradually and the intensity of the high orderharmonic generation increases. The intensity of the high order harmonic generation gets increasedby increasing the intensity of the laser, due to the opening of the gap for higher laser intensity, thusit becomes easier to tunnel ionization and compound nucleus, and so the intensity of the high orderharmonic generation increases.This submitted work is divided into four chapters. The first chapter introduces briefly thedevelopment of molecular reaction dynamics and the basic theory of high order harmonicgeneration. Chapter two presents the basic theory and method of wave-packet dynamics. In chapterthree we calculate the probability of dissociation and Coulomb explosion of hydrogen molecularion in the strong field, and further research the influence of laser parameters on dissociationprobability. In chapter four, we calculate the high order harmonic generation spectrum in thefemtosecond laser field. The investigations indicate that the high order harmonic generationspectrum in the strong laser field basically has the structure of falling-plateau-cutoff. The intensityof the high order harmonic generation in platform area becomes stronger with the increase of thevibrational quantum number. All phenomena are given reasonable explanation. |
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