title: Synchrotron-based valence shell photoionization of CH radical.
abstract: We report the first experimental observations of X(+) (1)Σ(+)←X (2)Π and a(+) (3)Π←X (2)Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg states of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: B
authors.initials: B
authors.lastname: Gans
authors.affiliation: Institut of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Holzmeier
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint Aubin BP 48, F-91192 Gif sur Yvette Cedex, France.
authors.forename: J
authors.initials: J
authors.lastname: Krüger
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: C
authors.initials: C
authors.lastname: Falvo
authors.affiliation: Institut of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Röder
authors.affiliation: Laboratoire de Chimie Physique, UMR 8000 CNRS-Univ. Paris-Sud, Univ. Paris-Saclay, Bât. 350, Centre Universitaire Paris-Sud, F-91405 Orsay Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Lopes
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint Aubin BP 48, F-91192 Gif sur Yvette Cedex, France.
authors.forename: G A
authors.initials: GA
authors.lastname: Garcia
authors.affiliation: Université Lille, CNRS, UMR 8522-PC2A-Physicochimie des Processus de Combustion et de l'Atmosphère, F-59000 Lille, France.
authors.forename: C
authors.initials: C
authors.lastname: Fittschen
authors.affiliation: Institut des Sciences Moléculaires, UMR 5255 CNRS-Université de Bordeaux, Bât. A12, 351 cours de la Libération, F-33405 Talence Cedex, France.
authors.forename: J-C
authors.initials: JC
authors.lastname: Loison
authors.affiliation: Laboratoire de Chimie Physique, UMR 8000 CNRS-Univ. Paris-Sud, Univ. Paris-Saclay, Bât. 350, Centre Universitaire Paris-Sud, F-91405 Orsay Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Alcaraz