Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C${}_2^{-}$

Abstract

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 $1\ddot{I}{ƒ}_u\to 3\ddot{I}{ƒ}_g$ and $1\ddot{I}{ƒ}_g\to 1\ddot{I}{€}_u$ 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~à 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${}_2^{-}$ $1\ddot{I}{ƒ}_u^{-1}3\ddot{I}{ƒ}_g^2{}^2\hat{I}{\pounds }_u^{+}$ and $1\ddot{I}{ƒ}_g^{-1}3\ddot{I}{ƒ}_g^2{}^2\hat{I}{\pounds }_g^{+}$ core-excited levels.

8 pages, 5 figures, 1 table, accepted for publication in ChemPhysChem