Raman and IR Studies on Proton-Related Dynamics in π -Molecular Crystals

Infrared absorbance (IR) spectra and Raman scattering spectra were measured as a function of pressure for molecular crystals of several 1,3-diketones, which are composed of hydrogen-bonded π -molecular chains. An unconventional proton-related band is commonly observed in the IR spectra around 1800-2000cm−1 in these compounds. We ascribed the observed band to proton vibration localized around kink-(or antikink-) solitons. The intensity of the band rapidly increases with application of hydrostatic pressure, suggesting increase in number of the solitons-like defects of the molecular chains via deformation of the double-well type proton potential.