Synthesis of ternary compound in H–S–Se system at high pressures*

Abstract

The chemical reaction products of elemental sulfur (S), selenium (Se), and molecular hydrogen (H2) at high pressures and room temperature are probed by Raman spectroscopy. Two known compounds H2S and H2Se can be synthesized after laser heating at pressures lower than 1 GPa. Under further compression at room temperature, an H2S–H2Se and an H2S–H2Se–H2 van der Waals compounds are synthesized at 4 GPa and 6 GPa, respectively. The later is of guest–host structure and can be identified as (H2S) x (H2Se)(2−x)H2. It can be maintained up to 37 GPa at least, and the stability of its H2Se molecules is extended: the H–Se stretching mode can be detected at least to 36 GPa but disappears at 22 GPa in (H2Se)2H2. The pressure dependence of S–H and Se–H stretching modes of this ternary compound is in line with that of (H2S)2H2 and (H2Se)2H2, respectively. However, its hydrogen subsystem only shows the relevance to (H2S)2H2, indicating that this ternary compound can be viewed as H2Se-replaced partial H2S of (H2S)2H2.