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Slow Photoelectron Spectroscopy of δ‐Valerolactam and Its Dimer
Author(s) -
Mahjoub Ahmed,
Hochlaf Majdi,
Poisson Lionel,
Nieuwjaer Nicolas,
Lecomte Frédéric,
Schermann JeanPierre,
Grégoire Gilles,
Manil Bruno,
Garcia Gustavo A.,
Nahon Laurent
Publication year - 2011
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100090
Subject(s) - photoionization , excited state , chemistry , autoionization , atomic physics , ground state , ionization , dimer , photoemission spectroscopy , population , ion , x ray photoelectron spectroscopy , physics , nuclear magnetic resonance , demography , organic chemistry , sociology
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 ${{\rm{\tilde X}}}$ 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 ${{\rm{\tilde X}}}$ ground, ${{\rm{\tilde A}}}$ , ${{\rm{\tilde B}}}$ and ${{\rm{\tilde C}}}$ 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.