Infrared study of hydrogen up to 310GPa at room temperature

We observed a strong difference of the pressure dependence of the infrared (IR) active molecular vibron of hydrogen in phase IV in the 200-310GPa pressure range in comparison with the Raman vibrons. While the Raman vibron strongly splits (approximate to 250cm(-1)) at the transition from phases III to IV at 220GPa, the IR vibron nearly does not change. This small spitting of IR vibron is not described by the graphene-like structure proposed for phase IV. The combined pressure dependence of Raman and IR vibrons provides a sensitive test for further theoretical models of phase IV.