Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C2−

Abstract

Carbon 1s core-hole excitation of the molecular anion C2− has been experimentally studied at high resolution by employing the photon-ion merged-beams technique at a synchrotron light source. The experimental cross section for photo–double-detachment shows a pronounced vibrational structure associated with (Formula presented.) and (Formula presented.) core excitations of the C2− ground level and first excited level, respectively. A detailed Franck-Condon analysis reveals a strong contraction of the C2− molecular anion by 0.2 Å upon this core photoexcitation. The associated change of the molecule's moment of inertia leads to a noticeable rotational broadening of the observed vibrational spectral features. This broadening is accounted for in the present analysis which provides the spectroscopic parameters of the C2− (Formula presented.) and (Formula presented.) core-excited levels.