Infrared study of sulphur at high pressures

Infrared absorption spectra of sulphur in diamond anvil cells at pressures up to 10 GPa are reported. Seven fundamental internal modes are observed and correlated with results on samples at atmospheric pressure and at low temperatures. Apart from some minor discontinuities near 5.3 GPa, the spectra show a smooth evolution with pressure, consistent with X-ray diffraction data. There is no evidence of a breakdown of the S8 ring molecules into chains, as deduced from several Raman studies. Changes in colour indicate a strong perturbation of electronic at higher pressures which may be related to phase transitions observed in the presence of intense laser radiation.