Fragmentation of Valence and Core-Shell (Cl 2p) Excited C₂Cl₄ Molecule

The dynamics of the photofragmentation pathways of tetrachloroethylene with photon energies from 15 up to 250 eV encompassing the Cl 2p edge is presented. In order to distinguish the fragmentation channels, the ionic fragments were separated according to their mass-to-charge ratio, measured in coincidence with the photoelectrons, and collected as a function of the incident photon energy. Distinct minima or maxima are found in the partial ion yield in the region between 40 and 50 eV. These features are believed to be associated with the Cooper minimum which results from a molecular orbital with a strong atomic 3p subshell character. In the shallow core region, some fragmentation patterns are considered in terms of fast fragmentation of the C₂Cl₄ molecule, despite the heavy mass of its fragments. In the present case, the fast fragmentation is favored by the very strong antibonding character of the LUMO, understandable in the frame of the core equivalent model for halogen-containing molecules. In addition, ab initio calculations were performed to obtain states at the Cl 2p edge. Singlet and triplet states at the Cl 2p edge of the C₂Cl₄ molecule, corresponding to the Cl(2p → 9b_1u*) and Cl(2p → 8b_2u*) transitions, were calculated in order to form a basis set of molecular states from which the spin-orbit splitting can be inferred. Multiconfigurational self-consistent field (MCSCF) calculation followed by multireference configuration interaction (MRCI) was the method chosen to establish a set of singlet and triplet states at the 2p excitation edge in addition to the ground state.