The mechanism of unimolecular dissocation reactions of carbon disulfide (CS2) has been studied theoretically. Analytic forms of potential energy surfaces were constructed using the results ofab initioconfiguration interaction (CI) calculations. A simplified rotationhyphen;vibration Hamiltonian was derived to carry out the classical trajectory calculations and to analyze the classical phase space structure of high vibrationally excited CS2molecule. It was found that two different types of trajectories, the normal mode type quasiperiodic and the chaotic trajectory, coexist even above the dissociation threshold. The vibrational energy levels, calculated by the semiclassical quantization for the normal mode type trajectories, showed a nearly equal spacing. Based on the results of present calculations, the possibility of mode selective infrared (IR) multiphoton excitations and dissociation were examined.
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