Structures and Dynamics of Negatively-Charged Molecular Clusters

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In the present study, we have concentrated our attention to (1) the geometrical and electronic structures and (2) reactivities of negatively-charged molecular clusters :(1) The electronic structures of [(CO_2)_nROH]^-(R=H,CH_3, and C_2H_5) were investigated by photoelectron spectroscopy. The analysis of the spectra revealed that two forms of isomers coexist in [(CO_2)_nROH]^-(2*n*3) ; one has an electronic structure described as [C_2O_4^-・ROH(CO_2)_<n-2>]where the excess electron is delocalized over two CO_2 molecules, and the other involves a monomer anionic core as [CO_2^-・ROH(CO_2)_<n-1>]. This is one of the few experimental rasults which demonstrates the coexistence of isomers of negatively-charged molecular clusters having defferent electronic structures. The present findings are also supported byab initio calculations at the unrestricted Hatree-Fock levels.(2) New type of gas-phase reactions involving nagatively-charged molecular clusters were investigated by mass spectrometric technique combined with photoelectron spectroscopy. For example, we have reported reactions of (CO_2)_n^-with CH_3I leading to the formation of a novel molecular anion [CO_2CH_3I]^-, which has not been observed in the corresponding condensed-phase reaction. It turned out that [CO_2CH_3I]^-has a large vertical detachment energy, implyintg that the excess electron is delocalized over [CO_2CH_3I]^-to form an acetate-iodine complex [CH_3CO_2-I]^-. This suggests that (CO_2)_n^-reacts with CH_3I via anucleophilic process. Ab initio calculations are under way to get information on the geometrical and electronic structures of [CO_2CH_3I]^-.