title: Photoelectron diffraction in methane probed via vibrationally resolved inner-valence photoionization cross-section ratios.
abstract: Vibrationally resolved photoionization of the 2a1 orbital in methane has been studied both experimentally and theoretically, over a wide range of photon energies (40-475 eV). A vibrational progression associated with the symmetric stretch mode of the 2a1(-1) single-hole state was observed in the experimental photoelectron spectra. Individual vibrational sub-states of the spectra were found to be best modeled by asymmetric line-shapes with linewidths gradually increasing with the vibrational quantum number. This indicates the occurrence of a pre-dissociation process for the involved ionic state, discussed here in detail. Finally, diffraction patterns were observed in the vibrational branching ratios for the first three vibrational sub-states ("v-ratios") of the experimental photoelectron spectra. They are found to be in excellent qualitative agreement with those obtained from ab initio models. Compared with previous studies of the 1a1(-1) core-shell photoionization of methane, the period of oscillation of the v-ratios is found to be very different and the phases are of opposite signs. This suggests a strong interplay between the electron diffraction and interference effects inside the molecular potential.
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France. saikat.nandi@synchrotron-soleil.fr.
authors.forename: Saikat
authors.initials: S
authors.lastname: Nandi
authors.affiliation: Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain.
authors.forename: Etienne
authors.initials: E
authors.lastname: Plésiat
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France. saikat.nandi@synchrotron-soleil.fr.
authors.forename: Minna
authors.initials: M
authors.lastname: Patanen
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France. saikat.nandi@synchrotron-soleil.fr and Extreme Light Infrastructure - Nuclear Physics (ELI-NP), 'Horia Hulubei' National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, RO-077125 Măgurele, Jud. Ilfov, Romania.
authors.forename: Catalin
authors.initials: C
authors.lastname: Miron
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France. saikat.nandi@synchrotron-soleil.fr.
authors.forename: John D
authors.initials: JD
authors.lastname: Bozek
authors.affiliation: Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain and Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nano), Cantoblanco, 28049 Madrid, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Martín
authors.affiliation: Dipartimento di Scienze Chimiche e Farmaceutiche, Universita di Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy. decleva@units.it.
authors.forename: Daniele
authors.initials: D
authors.lastname: Toffoli
authors.affiliation: Dipartimento di Scienze Chimiche e Farmaceutiche, Universita di Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy. decleva@units.it.
authors.forename: Piero
authors.initials: P
authors.lastname: Decleva