Liquid hydrogen structure factor to 5 GPa and evidence of a crossover between two density evolutions

International audienceThe center-of-mass structure factor, S(Q), of liquid hydrogen and liquid deuterium has been measured upto 5 GPa, mostly along the melting line from 50 to 296 K. Good quality data were achieved thanks to a novelsynchrotron x-ray technique that can isolate the very weak x-ray scattering signal of the micrometric volume ofhydrogen compressed in the diamond anvil cell. S(Q) is dominated by a broad peak and hence, its wave-vectorposition, Qm, is used to appreciate the structural changes in the system. An isotope effect in the position of Qmis observed that can be explained by a density effect. The shift of Qm towards higher Q as density increases isfollowed over a threefold compression. Two simple liquid type evolutions are disclosed with a crossover betweenthem around 37 nm−3/molecule. An interpretation is proposed based on the change in the zero-point motionalrenormalization of the interaction from anharmonic to harmoni