Anomalous Raman peaks of intra-molecular hydrogen bond material 5-bromo-9-hydroxyphenalenone under various pressure and temperature conditions

Studies on the Raman peaks appear at 593, 625, 651 and 1198cm(-1) in the intra-molecule hydrogen bond material 5-bromo-9-hydroxyphenalenone were performed under various pressure and temperature conditions. These peaks show two characteristic results: (1) in high pressure study, their pressure coefficients are approximately 4-6 times larger than those of other Raman peaks of this material, (2) in the latter experiment, they decrease in intensity with temperature and vanish around room temperature. These results support a model that these Raman peaks are generated by intra-molecule vibrations coupled with a proton tunneling motion.