Theoretical Studies on the Dynamics of Clusters and Excited States

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Reactions and dynamics of van der Waals molecules and metal clusters are topics of recent experimental and theoretical studies. In this research project, we have studied several subjects of these topics by quantumchemical methods. Some of them are as follows.(1) Potential energy curves of the round, excited, and ionized states of the Ven der Waals molecules such as Ar_2, Kr_2, ArF, and CsRg (Rg=Ne, Ar, Kr, Xe) are studied by the SAC/SAC-CI method. For Ar_2, the results for the 4s, and 4p Rydberg stated compare very well with the experimental results of the absorption and emission spectra. Some new assignments of the observed spectra are given, particularly for the excitations from the bound excited states. For the CsRg system, the SAC-CI potential curves and the (induced) transition moments have reproduced well the observed collision induced absorption spectra. We could then clarify the detailed electronic processes included in the observed collision induced absorption spectra.(2) The … More Exponentially Generated Wave Function (EGWF) method is proposed as a generalization of the SAC method. The excitator method applied to the EGWF method is proposed as a generalization of the SAC-CI method. These methods are applied to the various ground, excited, ionized, and anion states of C_2, CO, HF, etc at normal and elongated distances with very good agreement with the full CI (exact) solutions. The result implies that we have prepared the theory for the ground, excited, ionized, and anion states which is applicable for any states with arbitrary nuclear configurations. The method has also been shown to be powerful for multi-electron excitation and ionization processes.(3) Chemisorption of an oxygen molecule on a silver surface is studied theoretically with the use of the Dipped Adjuster Model (DAM) for Ag_xO_2 with x = 2 and 4. Electron correlation in low-lying surface states and electron transfer from bulk metal are described by combining DAM with the symmetry-adapted cluster (SAC) CI method. For chemisorption, electron transfer from the bulk metal to the Adjuster and the electrostatic image force are important. They cannot be treated by the conventional cluster model, but are dealt with by the DAM. Three lowlying states, ^2A_1, ^2A_2, and ^2B_1 of the adclusters of Ag_2O_2^- and Ag_4O_2^- are involved in the chemisorption process. In the molecular adsorption state, the ^2A_1 state is assigned to peroxide (O_2^<2->) species and the ^2A_2 and ^2B_1 states to superoxide (O_2^-) species. The 0-0 stretching frequencies are in good agreement with the experimental values. In the potential energy curves of Ag_4O_2^-, another potential minimum corresponding to th e dissociative adsorption state is obtained for the ^2A_1 state. The ener-getics of the molecular and dissociative adsorptions show reasonable agreement with experiments. Less