  Bound-bound transitions can occur when localized atomic orbitals are
thermally depleted, allowing excitations that would otherwise be forbidden at
zero temperature. We predict signatures of bound-bound transitions in x-ray
Thomson scattering measurements of laboratory-accessible warm dense conditions.
Efficient average-atom models amended to include quasibound states achieve
continuity of observables under ionization and agree with time-dependent
density functional theory in their prediction of these scattering signatures,
which hold compelling diagnostic potential for high-energy-density experiments.
