NEXAFS and MS-AES spectroscopy of the C 1s and Cl 2p excitation and ionization of chlorobenzene: Production of dicationic species.

We report on single- and double-charge photofragment formation by synchrotron radiation, following C 1s core excitation and ionization and Cl 2p inner excitation and ionization of chlorobenzene, CHCl. From a comparison of experimental near-edge X-ray absorption fine structure spectra and theoretical calculations, the nature of various core and inner shell transitions of the molecule and pure atomic features were identified. To shed light on the normal Auger processes following excitation or ionization of the molecule at the Cl 2p or C 1s sites, we addressed the induced ionic species formation. With energy resolved electron spectra and ion time-of-flight spectra coincidence measurements, the ionic species were correlated with binding energy regions and initial states of vacancies. We explored the formation of the molecular dication CHCl, the analogue benzene dication CH, and the singly charged species produced by single loss of a carbon atom, CHCl. The appearance and intensities of the spectral features associated with these ionic species are shown to be strongly site selective and dependent on the energy ranges of the Auger electron emission. Unexpected intensities for the analogue double charged benzene CH ion were observed with fast Auger electrons. The transitions leading to CHCl were identified from the binding energy representation of high resolution electron energy spectra. Most CHCl ions decay into two singly charged moieties, but intermediate channels are opened leading to other heavy dicationic species, CH and CHCl, the channel leading to the first of these being much more favored than the other.