title: Experimental and ab initio characterization of HC3N+vibronic structure. I. Synchrotron-based threshold photo-electron spectroscopy.
abstract: Threshold-photoionization spectroscopy of cyanoacetylene (HC3N) and its15N isotopologue has been investigated in the vacuum-ultraviolet range with a synchrotron-based experiment allowing to record threshold-photoelectron spectrum and photoion yield over a large energy range (from 88 500 to 177 500 cm-1, i.e., from 11 to 22 eV). Adiabatic ionization energies towards the three lowest electronic states X+2Π, A+Σ+2, and B+Π2 are derived from the threshold-photoelectron spectrum. A detailed description of the vibrational structure of these states is proposed leading to the determination of the vibrational frequencies for most modes. The vibrational assignments and the discussion about the electronic structure are supported by multireference ab initio calculations (CASPT2, MRCI). Unprecedented structures are resolved and tentatively assigned in the region of the B+← X transition. Exploratory calculations highlight the complexity of the electronic landscape of the cation up to approximately 10 eV above its ground state.
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS UMR 8214, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Desrier
authors.affiliation: Laboratoire de Chimie Physique, CNRS UMR 8000, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay Cédex, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Romanzin
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS UMR 8214, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lamarre
authors.affiliation: Laboratoire de Chimie Physique, CNRS UMR 8000, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay Cédex, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Alcaraz
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS UMR 8214, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: Bérenger
authors.initials: B
authors.lastname: Gans
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS UMR 8214, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: Dolores
authors.initials: D
authors.lastname: Gauyacq
authors.affiliation: Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, CP 160/09, B-1050 Bruxelles, Belgium.
authors.forename: Jacques
authors.initials: J
authors.lastname: Liévin
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS UMR 8214, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
authors.forename: Séverine
authors.initials: S
authors.lastname: Boyé-Péronne