Ultrahigh Pressure Studies of Hydrogen and Its Isotopes

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9701500 Silvera This is a new proposal to study solid hydrogen and its isotopes, deuterium and HD in the multimegabar pressure range. Pressures will be extended beyond 300 GPa, where it is believed that the dissociative transition to atomic metallic hydrogen will take place. This will be accomplished using high quality, small culet diamonds in newly designed precision diamond anvil cells. Transitions will be searched for by studying the strong IR absorption, as well as the Raman scattering from vibron modes, in the A-phase which is believed to precede the transformation to the atomic solid. A detected phase transition will then be studied by optical techniques to observe Drude free-electron behavior, or dc electrical conductivity at low temperature, in order to determine the conductive state. NMR will be used to determine ortho-para conversion rates. Optical techniques will be developed to determine the index or refraction and the equation of state. %%% This is a new proposal to study solid hydrogen and its isotopes, deuterium and HD in the multimegabar pressure range. Solid hydrogen and its isotopes have fascinating high pressure phase diagrams. These molecular solids are predicted to become molecular metals at pressures between 1.5 and 3 megabar and atomic metals at higher pressures. The molecular and atomic metals are predicted to be possible room temperature superconductors. A transition to a phase called the A-phase at about 1.5 megabars is still not understood. These solids will be studied at multimegabar pressures using newly designed precision diamond anvil cells. IR absorption, as well as Raman scattering will be used to search for new phases. These will then be studied by optical techniques or dc electrical conductivity at low temperature to observe possible metallic behavior. NMR will be used to determine ortho-para conversion rates. Optical techniqu es will also be developed to determine the index of refraction and the equation of state. ***