Progress in simple molecular mixtures under pressure

Investigations of simple molecular systems are important for fundamental understanding of intermolecular interactions, pressure-induced chemistry, the creation of new materials, and earth and planetary science. Recent studies have focused on the effects of pressure on the physics and chemistry of mixing, developing accurate equations of state, and potential chemical reactions in the tens of gigapascal pressure range using diamond-anvil cell techniques. In particular, these studies are crucial for interpreting high P-T dynamic compression experiments, where precise knowledge of pre-compression conditions is essential for the accurate determination of the final state in both ramp compression and Hugoniot experiments. New experiments include measurements of the acoustic velocities and ρ-P equations of state for systems such as H2:He and D2/H2:CO2 mixtures using Brillouin spectroscopy. We characterized the chemical and physical properties of these systems through Raman and infrared spectroscopy as well as x-ray diffraction and compared them with first-principles calculations. The results provide evidence for new chemical reactions and constraints on the phase diagrams for these systems.