Momentum Transfer Dependence of Inelastic X-Ray Scattering from the LiKEdge

Inelastic x-ray scattering from the K edge of lithium metal at 30 K is measured at momentum transfers q0ex0ex=0ex0ex8.8 and 97.3nm^-1 with 80 meV energy resolution. The transition from dipolar ( 1s→p, q0ex0ex=0ex0ex8.8nm^-1) to monopolar ( 1s→s, q0ex0ex=0ex0ex97.3nm^-1) excitations is demonstrated by differences in the spectra reflecting either the p or s partial density of states above the Li Fermi level. The Mahan-Nozi\`eres-De Dominicis theory is utilized to determine both threshold exponents α₀ and α₁ from the present K-edge data.