High-pressure measurements of hydrogen phase IV using synchrotron infrared spectroscopy
Chang-sheng Zha, Zhenxian Liu, Muhtar Ahart, Reinhard Boehler, and Russell J. Hemley
Accepted
Phase IV of dense solid hydrogen has been identified by its infrared spectrum using highpressure synchrotron radiation techniques. The spectrum exhibits a sharp vibron band at higher frequency and lower intensity than that for phase III, indicating the stability of molecular H2 with decreased intermolecular interactions and charge transfer between molecules. A low-frequency vibron having a strong negative pressure shift indicative of strongly interacting molecules is also observed. The character of the spectrum is consistent with an anisotropic, mixed layer structure related to those recently predicted theoretically. Phase IV was found to be stable from 220 GPa (300 K) to at least 340 GPa (above 200 K), with the I-III-IV triple point located. Infrared transmission observed to the lowest photon energies measured place constraints on the electronic properties of the phase.