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

Carbon 1s core-hole excitation of the molecular anion C-2(-) 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 1 sigma u -> 3 sigma g ${1\sigma _u \to 3\sigma _g }$ and 1 sigma g -> 1 pi u ${1\sigma _g \to 1\pi _u }$ core excitations of the C-2(-) ground level and first excited level, respectively. A detailed Franck-Condon analysis reveals a strong contraction of the C-2(-) molecular anion by 0.2 angstrom 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 C-2(-) 1 sigma u-13 sigma g22 sigma u+ ${1\sigma _u<^>{ - 1} \,3\sigma _g<^>2 \;<^>2 \Sigma _u<^> + }$ and 1 sigma g-13 sigma g22 sigma g+ ${1\sigma _g<^>{ - 1} \,3\sigma _g<^>2 \;<^>2 \Sigma _g<^> + }$ core-excited levels.