Molecular dissociation and two low-temperature high-pressure phases of H₂S

We performed powder x-ray experiments on hydrogen sulfide (H₂S) under high pressure at room and low temperatures. Phase V appearing above 27 GPa at room temperature was confirmed by x ray to be associated with a molecular dissociation. The molecular dissociation was first observed at 150 K at a higher pressure around 43 GPa. Two new low-temperature high-pressure phases III′ and IV′ were discovered. Spiral chains of sulfur atoms are found in both phases as well as in phase IV.