Effective Volumetric Factor for Inhomogeneous Temperature in Volumetric Measurements of Gas Absorption and Desorption

Accounting of effective volumetric factor for the measurement at inhomogeneous temperature allows to the simplify the measurement process avoiding a pre-calibration with a noble gas. The volumetric correction in form of the volumetric factor is calculated analytically by modeling of the temperature profile in the volumetric apparatus, and provides a quite agreement with the measured results. The calculation can be applied for each volumetric measurement with an inhomogeneous temperature distribution

Semimetallic molecular hydrogen at pressure above 350 GPa

According to the theoretical predictions, insulating molecular hydrogen dissociates and transforms to an atomic metal at pressures P~370-500 GPa. In another scenario, the metallization first occurs in the 250-500 GPa pressure range in molecular hydrogen through overlapping of electronic bands. The calculations are not accurate enough to predict which option is realized. Here we show that at a pressure of ~360 GPa and temperatures <200 K the hydrogen starts to conduct, and that temperature dependence of the electrical conductivity is typical of a semimetal. The conductivity, measured up to 440 GPa, increases strongly with pressure. Raman spectra, measured up to 480 GPa, indicate that hydrogen remains a molecular solid at pressures up to 440 GPa, while at higher pressures the Raman signal vanishes, likely indicating further transformation to a good molecular metal or to an atomic state