Molecular fragmentation following photon excitation of core electrons from K shells of C and O and L shell of S atoms forming the OCS molecule was studied. Emerging photoelectrons and charged fragments were detected in coincidence. Application of time-of-flight spectroscopy together with triple coincidence photoelectron-photoion-photoion, double coincidence photo-electron-photoion and photoion-photoion techniques allow a detailed insight into the geometry and the dynamics of the de-excitation processes and an unambiguous assessment of all fragmentation channels of highly excited molecules. Such studies are of major interest in fundamental research and they are relevant also in environmental, biological and technological investigations.
Our group has recently carried out measurements of dispersed fluorescence from photo-excited N_{2} and CO molecules in 19-34 eV excitation energy range using the Swedish synchrotron radiation facility MAX in Lund. The experimental results show that relative intensities of the fluorescence from different vibrational levels of the excited N_{2}^{+} and CO^{+} vary with the excitation energy. We associate this phenomenon with the existence of doubly excited states in N_{2} and CO in the corresponding energy regions. Our results show that the widths of the newly revealed states correspond to their lifetimes of the order of few femtoseconds.
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