Dissociation energy of neutral and ionic benzene-noble gas dimers by pulsed field threshold ionization spectroscopy

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Abstract
Delayed pulsed field threshold ionization of clusters excited to high long‐lived Rydberg states is used to study their dissociation behavior. Benzene–Ar and benzene–Kr dimers are excited by resonance enhanced two‐photon ionization to Rydberg levels close to various ionization thresholds. The field ionized threshold ions are monitored and separated from the non‐energy‐selected ions in a reflecting field mass spectrometer with high mass resolution. The appearance of threshold ions at the daughter ion mass indicates the onset of a dissociation process. Daughter ions are first observed for the 16161(3/2) level of the two investigated dimers. This leads to an upper limit of the dissociation energy of benzene–Ar of 340 cm−1 which is probably higher than the true dissociation energy. For the first time threshold ions are observed for large internal energies of some 5 eV in the core indicating that high Rydberg states maintain their long lifetime even if the core is electronically or vibrationally excited by several eV.