High pressure ultraviolet-visible-near infrared study of colored solid hydrogen sulfide

Optical absorption measurements at high pressure were extended up to 5.5 eV in the ultraviolet region by constructing an ultraviolet-visible-near infrared absorption spectrometer adapted for diamond anvil cells and by using impurity free synthetic diamonds. Using the improved spectrometer, absorption spectra of solid hydrogen sulfide (H2S) were measured under various pressures from 0.3 to 29 GPa at room temperature. The band gap estimated from the absorption edge was 4.8 eV at 0.3 GPa and decreased to 2.7 eV at 29 GPa almost linearly except for a small jump at about 11 GPa corresponding to the phase transition to phase IV. At the same pressure, an Urbach tail responsible for the coloring of the solid H2S suddenly appeared. Raman signals excited with a green Ar ion laser (2.41 eV) were found to increase in intensity with pressure, which was explained by preresonance Raman effects induced by the decreasing of the gap energy near to the Raman excitation energy. (C) 2002 American Institute of Physics.