FIRST INELASTIC X-RAY-SCATTERING SPECTROSCOPY MEASUREMENTS OF THE DYNAMIC STRUCTURE FACTOR S(Q,OMEGA) OF ELECTRONS IN A SOLID NOBLE-GAS (HE)

Inelastic x-ray scattering spectroscopy measurements on hcp single crystal solid He with q∥c axis and q=0.45, 0.97, and 1.24 a.u. are presented. The crystals were grown in situ under a pressure of 600 bar at 5-7 K within a Be hollow cylinder. By subtracting a measurement on the empty Be cylinder, pure solid He spectra are obtained and discussed in terms both of the hcp He band structure and of excitonic excitation. The existence of an exciton at 21.8 eV above the 1s core level could unambiguously be settled. Clear evidence is found that the bottom of the conduction band is at 27 eV. © 1995 American Institute of Physics.