Infrared Spectra of Benzene at High Pressures

Mid-infrared spectra in the ranges 400-1800 and 2700-4000 cm^-1 are reported for benzene samples in diamond anvil cells at ambient temperature and pressures up to 10 GPa. The freezing pressure is confirmed to be 0.1±0.05 GPa. Changes in the spectra and in the sample appearance indicate that sluggish solid state phase transitions occur near 2.0 and 4.0 GPa. The wave number shifts with pressure for 27 selected peaks are plotted. Their small increases show that only minor distortions of the molecules occur, and there is no evidence of any weakening of intramolecular bonds in this pressure range.