Melting line and fluid structure factor of oxygen up to 24 GPa

Using synchrotron x-ray diffraction and Raman spectroscopy, we have measured the structural properties of dense fluid O2 up to 24 GPa. A quantitative evolution with pressure of the structure factor of a low-Z molecular fluid is obtained here for the first time under pressure. No evidence of molecular association is observed here in contrast to what has been observed in the cryo-O2 fluid or in the solid above 12 GPa. The melting curve, which can evidence structural changes in the fluid or the solid, has also been measured up to 750 K by direct visualization of the solid-fluid equilibrium. No unusual behavior is observed hence invalidating a previous report