RAMAN-SCATTERING OF CUGEO3 AND Y2BANIO5

Raman scattering and infrared absorption spectra of CuGeO3 and Y2BaNiO 5 have been measured. CuGuO(3) is a typical inorganic spin-Peierls sys tem with S=1/2 and Y2BaNiO5 is a recently discovered Haldane system wi th S=1. Two magnon excitation along the c-axis is found for CuGeO3. A dditional two-magnon excitations due to one dimensional fluctuation ar e observed for both system. For CuGeO3 the mode at about 30cm(-1) is t he soft mode due to the lattice distortion, not due to the spill gap. Tile normal mode calculations for CuGeO3 show that the crystal structu re is stabilized by the Ge-O frame.