title: Slow photoelectron spectroscopy of δ-valerolactam and its dimer.
abstract: We studied the single-photon ionization of gas-phase δ-valerolactam (piperidin-2-one) and of its dimer using vacuum-ultraviolet (VUV) synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. The slow photoelectron spectrum (SPES) of the monomer is dominated by the vibrational transitions to the ͠X state. Moreover, several weaker and complex bands are observed, corresponding to the population of the vibrational bands (pure or combination) of the electronically excited states of the cation arising from their mutual vibronic interactions. For the dimer, we measure a unique large band. These spectra are assigned with the help of theoretical calculations dealing with the equilibrium geometries, electronic-state patterns and evolutions, harmonic and anharmonic wavenumbers of the monomer and dimer, either neutral or positively charged. The state energies of the [δ-valerolactam](+) cation in the ͠X ground, ͠A, ͠B, ͠C, excited electronic states, and of the [δ-valerolactam](2) (+) cation's lowest states are determined. After its formation, [δ-valerolactam](2) (+) is subject to intramolecular isomerization, H transfer and then unimolecular fragmentation processes. Close to the ionization thresholds, the photoionization of these molecules is found to be mainly dominated by a direct process whereas the indirect route (autoionization) contributes at higher energies.
authors: Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée, France.
authors: Ahmed
authors: A
authors: Mahjoub
authors: Majdi
authors: M
authors: Hochlaf
authors: Lionel
authors: L
authors: Poisson
authors: Nicolas
authors: N
authors: Nieuwjaer
authors: Frédéric
authors: F
authors: Lecomte
authors: Jean-Pierre
authors: JP
authors: Schermann
authors: Gilles
authors: G
authors: Grégoire
authors: Bruno
authors: B
authors: Manil
authors: Gustavo A
authors: GA
authors: Garcia
authors: Laurent
authors: L
authors: Nahon