  We report on the Cu 1s resonant inelastic X-ray scattering (RIXS) of Cu-O
one-dimensional (1D) strongly correlated insulator systems with contrasting
atomic arrangements, namely edge-sharing CuGeO3 and corner-sharing Sr2CuO3.
Owing to good statistics of the high-resolution RIXS data, so far unresolved
fine structures are revealed. Detailed photon-energy and momentum dependence of
the RIXS spectra in comparison with theoretical calculations has clarified the
natures of the low-energy charge excitations and hybridization of the
electronic states.
