The relationship between quantum scattering states, continuous energy spectra, and unbounded motion is a fundamental defining property of scattering theory in quantum mechanics, making it common knowledge that does not require citation.
The claim states a textbook definition from quantum mechanics: scattering states correspond to continuous energy spectra and unbounded motion (as opposed to bound states, which have discrete spectra and localized/bounded motion). None of the retrieved papers specifically address or test this foundational definition as a novel empirical hypothesis; rather, it is basic physical common knowledge.