Coherent Anti-Stokes Raman Spectroscopy of Highly Compressed Solid Deuterium at 300 K: Evidence for a New Phase and Implications for the Band Gap

Coherent anti-Stokes Raman spectroscopy has been used to study deuterium at ambient temperature to 187 GPa, the highest pressure this technique has ever been applied. The pressure dependence of the ν₁ vibron line shape indicates that deuterium has a ρdirect=0.501 and ρexciton=0.434 mol/cm³ for a band gap of 2ωP=4.66 eV. The extrapolation from the ambient pressure band gap yields a metallization pressure of 460 GPa, confirming earlier measurements. Above 143 GPa, the Raman shift data provide clear evidence for the presence of the ab initio predicted I^' phase of deuterium.