We consider the energy weighted sums (EWS) for isovector giant dipole
resonances (IVGDR) in finite nuclei within Landau kinetic theory. The
dependence of both IVGDR energy, EIVGDR​, and the EWS enhancement factor,
κ(A), on the mass number A occurs because of the boundary condition
on the moving nuclear surface. The values of EIVGDR​A1/3 and κ(A) increase with A. The obtained value of the enhancement factor is about
10% for light nuclei and reaches approximately 20% for heavy nuclei. A fit of
the enhancement factor to the proper experimental data provides a value for the
isovector Landau amplitude of F1′​≃1.1.Comment: 14 pages, 3 figures, revised version, published in Phys. Rev. C79,
024321 (2009