Bromine metallization studied by X-ray absorption spectroscopy

Bromine has been studied up to a pressure of 110 GPa by X-ray absorption sp ectroscopy (XAS) at the bromine K-edge, that allows to measure the pressure evolution of the width of the unoccupied conduction band. At 25 +/- 5 GPa we observe a slope change in the evolution of this width. Comparison with p ublished calculations of the electronic density of states indicates that th e physical origin of the slope change is compatible with the metallisation process. This is also confirmed by a simple tight binding calculation. In a ddition, the metallisation pressure value is in agreement with calculated o nes. At 68+/-5 GPa a discontinuity in the evolution of the width of the sig ma antibonding band points out the onset of a phase transformation. This re sult is compatible with the observed phase transformation near 80 +/- 5 GPa by X-ray diffraction that is associated with the molecular dissociation.