Photophysics of molecular transition metal compounds studied by inner-shell excitation

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There are several planar complexes with two-dimensional structures in the transition metal compounds showing various physical properties. Details of photophysics, especially, inner-shell excitation and decay dynamics, of molecular transition metal compounds have not yet been revealed. In this work, we have been establishing fundamentals of the inner-shell spectroscopy applied to reveal photophysics of the molecular transition metal compound, by using 2p core spectroscopy of transition metals involving polarized photoabsorption and resonant photoelectron and soft x-ray emission since three years ago. The followings are new results from this work : 1) Electron correlation is reduced in the molecular transition metal compound, due to the covalent bond between the metal and ligand molecule. 2) Extraordinarily stronger satellite bands are observed according to stronger covalent bonds, and are assigned to the excitation from the metal to ligand unoccupied orbital. Polarized spectra have clearly shown that the ligand unoccupied orbital has 兀 * character. 3) We can evaluate the strength of the covalent bond by using the relative intensity of the satellite bands. 4) It is for the first time found that the kinetic energy of the photoelectron decreases as the photon energy increases in the satellite region. This means that the satellite bands arise from the single, or excitonic, excitation but does not from the electron correlation. The photon energy dependence of the electron kinetic energy is dependent on the molecular interaction among molecular transition metal compounds in the solid. Metallic systems show no dependence. 5) The high-spin molecular transition metal compounds do not show such dependence. This is due to the electron correlation, which becomes important in the high-spin compound. 6) It is revealed for the first time that resonant soft x-ray emission of molecular transition metal compounds show metal-to-ligand charge transfer bands.