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Abstract

Establishing metallic hydrogen is a goal of intensive theoretical and experimental work since 1935 when Wigner and Hungtinton [1] predicted that insulating molecular hydrogen will dissociate at high pressures and transform to a metal. This metal is predicted to be a superconductor with very high critical temperature [2]. In another scenario, the metallization can be realized through overlapping of electronic bands in molecular hydrogen in the similar 400 - 500 GPa pressure range [3-5]. The calculations are not accurate enough to predict which option will be realized. Our data are consistent with transforms of hydrogen to semimetal by closing the indirect band gap in the molecular phase III at pressure ~ 360 GPa. Above this pressure, the metallic behaviour in the electrical conductivity appears, the reflection significantly increases. With pressure, the electrical conductivity strongly increases as measured up to 440 GPa. The Raman measurements evidence that hydrogen is in the molecular phase III at pressures at least up to 440 GPa. At higher pressures measured up to 480 GPa, the Raman signal gradually disappears indicating further transformation to a good molecular metal or to an atomic state.