title: Identifying and Understanding Strong Vibronic Interaction Effects Observed in the Asymmetry of Chiral Molecule Photoelectron Angular Distributions.
abstract: Electron-ion coincidence imaging is used to study chiral asymmetry in the angular distribution of electrons emitted from randomly-oriented enantiomers of two molecules, methyloxirane and trifluoromethyloxirane, upon ionization by circularly polarized VUV synchrotron radiation. Vibrationally-resolved photoelectron circular dichroism (PECD) measurements of the outermost orbital ionization reveal unanticipated large fluctuations in the magnitude of the forward-backward electron scattering asymmetry, including even a complete reversal of direction. Identification and assignment of the vibrational excitations is supported by Franck-Condon simulations of the photoelectron spectra. A previously proposed quasi-diatomic model for PECD is developed and extended to treat polyatomic systems. The parametric dependence of the electronic dipole matrix elements on nuclear geometry is evaluated in the adiabatic approximation. It provokes vibrational level dependent shifts in amplitude and phase, to which the chiral photoelectron angular distributions are especially sensitive. It is shown that single quantum excitation of those vibrational modes, which experience only a relatively small displacement of the ion equilibrium geometry along the normal coordinate and which are then only weakly excited in the Franck-Condon limit, can be accompanied by big shifts in scattering phase; hence the observed big fluctuations in PECD asymmetry for such modes.
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin BP 48, 91192, Gif sur Yvette, France.
authors.forename: Gustavo A
authors.identifier: http://orcid.org/0000-0003-2915-2553
authors.initials: GA
authors.lastname: Garcia
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin BP 48, 91192, Gif sur Yvette, France.|Current address: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Institut Parisien de Chimie Moléculaire (IPCM), 4 Place Jussieu, 75252, Paris Cedex 05, France.
authors.forename: Héloïse
authors.identifier: http://orcid.org/0000-0003-4844-229X
authors.initials: H
authors.lastname: Dossmann
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin BP 48, 91192, Gif sur Yvette, France.
authors.forename: Laurent
authors.identifier: http://orcid.org/0000-0001-9898-5693
authors.initials: L
authors.lastname: Nahon
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK.|Current address: Institut Lumiere Matière, UMR5306, CNRS, Université Lyon 1, 69622, Villeurbanne, France.
authors.forename: Steven
authors.initials: S
authors.lastname: Daly
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: Ivan
authors.identifier: http://orcid.org/0000-0002-7941-9079
authors.initials: I
authors.lastname: Powis
keywords: circular dichroism; photoelectron circular dichroism; photoelectron spectroscopy; photoionization; photophysics