In the light of recent work on shape resonances in diatomic systems, the question of a possible persistence of atomic centrifugal barrier effects in molecules arises, particularly as regards resonant penetration of f-waves. Experim ents on selenium vapour suggest th a t two cases may be expected depending on whether localized f states are present or not in the atom. The evidence in Se is th a t f waves mainly external to the atom are scattered into several channels by the anisotropic molecular

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... ield and th a t damping of the f-maximum results. A reason is suggested for which inner shell absorption spectra of solids may not faithfully reproduce the density of states of the conduction band, even for elemental materials.