Pressure dependence of the vibron modes in solid hydrogen and deuterium

Abstract
It has long been speculated that the high-pressure softening of the Raman-active vibron in hydrogen is a precursor of metallization. We use data for hydrogen, our new results for deuterium, and an established theory of the infrared- and Raman-active modes, to show that the softening of the Raman mode is due to the intermolecular potential and that it is the behavior of the ir mode which is crucial in considerations of metallization.