Vibrational structures in electron CO2scattering below the2 ushape resonance

Structures of vibrational origin were discovered in vibrationally inelastic electron–CO 2 cross sections in the energy range 0.4–0.9 eV, well below the 2 Π u shape resonance. They appear in the excitation of higher vibrational levels, in particular the highest members of the Fermi polyads of the type ( n , 2 m , 0) with n + m = 2–4. The lowest two structures, at 0.445 and 0.525 eV, are narrow; higher-lying structures are broader and boomerang-like. The structures are absent when the antisymmetric stretch is co-excited. The structures are interpreted in terms of a wavepacket of the nuclei reflected from a potential surface of the CO 2 − anion in a bent and stretched geometry. A state emerging from the virtual state upon bending and stretching and the state resulting from bending the 2 Π u shape resonance are discussed as possibly being responsible for the structures.