Synchrotron infrared spectroscopy to 0.15 eV of H2 and D2 at megabar pressures.

New synchrotron infrared absorption and reflectivity techniques have been developed to test predicted band overlap metallization in H 2 and D2 above 150 GPa at various temperatures. Measurements on both isotopes to maximum pressures of 216 GPa show no evidence for Drude excitations in the midinfrared to near-infrared spectrum. The most definitive are measurements on D 2, which remains transparent down to 0.15 eV at 170 GPa and 83 K. The results put new bounds on the optical conductivity and possible band-gap closure at the 150-GPa transition. In addition to strong vibrational transitions, new infrared absorption features are observed.