| People's life and production have been deeply affected by the laser. Some important parameters of the laser play an important part in the study of matter-laser interaction, for example, the intensity of the laser. With the development of the ultrashort intense laser technology, the short-pulse laser with the maximun energy about 1020W/cm2 can be obtained in recent experiments, which prompt the research on the interaction between materials and intense laser field. The studying on the atom, molecule and cluster physics of intense laser field become the very interesting and excited new topic in the basic theoretical research. Because the laser technology is employed in experiments, it is possible to observe the transient process of atoms or molecules in an intense laser pulse, which brings on the development of modern laser chemistry, for example, the femtosecond chemistry. Recently, the femtosecond laser technology is developed, which makes it possible that the evolvement of reaction transition-state, the space configuration of transition-state and the vector relation of the molecules of chemical reaction are real time observed on experiment, and that the laws of chemic reaction are known deeply. These requirements on experiment promote the theoretical research of the dynamic process of the interaction of atoms or molecules in ultrashort intense pulse, and make it one of the very active research fields. With the development of laser technology, the laser intensity which could be obtained is stronger and stronger. The corresponding electric field strength is far greater than that of the Coulomb electric field in the atom. Therefore the traditional perturbation method which treated the laser field as perturbation fail or become impractical, one has to turn to other means of calculation. Solving numerically the time-dependent Schr?dinger equation (TDSE) is one of the popular and the reasonable methods in present theoretical research. It is still impossible to numerically solve the time-dependent Schr?dinger equation for the molecules or multi-electron atoms under the intense laser fields even if the best computer of today is used. So the classical theory (CT) is used to study the dynamic behavior of the molecules and atoms in the intense laser pulse. The classical theory is adopted to study the questions of molecular dynamics, and it is to solve numerically the Newton equation or the Hamilton canonical equation. It is a convenience and effective method to solve numerically Hamilton canonical equation by the symplectic method. There is symplectic structure in the Hamiltonian system. The symplectic structure of the Hamiltonian canonical equation can be conserved during symplectic transformation. Therefore, in the early 1980's, Ruth and Feng Kang presented the symplectic algorithm for solving the Hamiltonian system, and found a new method for solving the Hamiltonian mechanics. After that many people have done much contribution on this research. Now people have applied the symplectic algorithm to many fields. The symplectic algorithm is widely applied on the research about the chemic reaction dynamic and molecular dynamic. Leimkuhler pointed out that the vibration Newton model could be used in molecular dynamic simulation, and it brings on the Hamilton canonical equation which is reasonablely to be numerically solved by symplectic algorithm. Yanxin Li and Aimin Shi reported that the symplectic algorithm was used to compute the classical trajectories of the A2B molecule model and diatomic molecule system separately. The computation by symplectic algorithm makes the computation time be extended 1-2 magnitude than the non-symplectic, which demonstrates fully the advantage of symplectic algorithm. Diatomic system is the simplest molecular system, lots of large molecule systems can be regarded as the combination of diatomic systems. So, it is very interesting to investigate the classical dissociation...
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