title: Dissociative double-photoionization of butadiene in the 25-45 eV energy range using 3-D multi-coincidence ion momentum imaging spectrometry.
abstract: Dissociative double-photoionization of butadiene in the 25-45 eV energy range has been studied with tunable synchrotron radiation using full three-dimensional ion momentum imaging. Using ab initio calculations, the electronic states of the molecular dication below 33 eV are identified. The results of the measurement and calculation show that double ionization from π orbitals selectively triggers twisting about the terminal or central C-C bonds. We show that this conformational rearrangement depends upon the dication electronic state, which effectively acts as a gateway for the dissociation reaction pathway. For photon energies above 33 eV, three-body dissociation channels where neutral H-atom evaporation precedes C-C charge-separation in the dication species appear in the correlation map. The fragment angular distributions support a model where the dication species is initially aligned with the molecular backbone parallel to the polarization vector of the light, indicating a high probability for double-ionization to the "gateway states" for molecules with this orientation.
authors.affiliation: Department of Physics, Division of Synchrotron Radiation Research, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
authors.forename: Shabnam
authors.initials: S
authors.lastname: Oghbaie
authors.affiliation: Department of Physics, Division of Synchrotron Radiation Research, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Gisselbrecht
authors.affiliation: Department of Physics, Division of Synchrotron Radiation Research, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
authors.forename: Joakim
authors.initials: J
authors.lastname: Laksman
authors.affiliation: Department of Physics, Division of Synchrotron Radiation Research, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
authors.forename: Erik P
authors.initials: EP
authors.lastname: Månsson
authors.affiliation: Department of Physics, Division of Synchrotron Radiation Research, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Sankari
authors.affiliation: Department of Physics, Division of Synchrotron Radiation Research, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
authors.forename: Stacey L
authors.initials: SL
authors.lastname: Sorensen