Abstract: A classical trajectory method is used to study a diatomic molecule(HF) interacting with chirped intense laser pulses.In the model,the motion of nuclei is described with classical Hamiltonian canonical equations.The Hamiltonian equation is solved numerically by a symplectic method,and the initial conditions are chosen by a single trajectory in the field-free case at random.The classical dissociation of HF by chirped pulses is evaluated.The dissociation probabilities with different laser intensities are discussed.Dissociation probabilities at different initial states are also investigated.The dissociation process is illustrated by classical phase trajectories and energy versus nuclei separation.

Key words: diatomic system, classical trajectory approach, symplectic algorithm