Isotope Effects in the Predissociation of Excited States of N(2)(+) Produced by Photoionization of (14)N(2) and (15)N(2) at Energies Between 24.2 and 25.6 eV

Photoelectron/photoion imaging spectrometry employing dispersed VUV radiation from the SOLEIL synchrotron has been used to study the predissociation of N(2)(+) states located up to 1.3 eV above the ion's first dissociation limit. Branching ratios for unimolecular decay into either N(2)(+) or N(+) were obtained by measuring coincidences between threshold electrons and mass-selected product ions, using a supersonic beam of either (14)N(2) or (15)N(2) as photoionization target. The results confirm that predissociation of the [Formula: see text] state of (14)N(2)(+) is faster than emission to the electronic ground-state by a factor 10 or more for all vibrational levels v′ ≥ 3, while for (15)N(2)(+) the two decay modes have comparable probabilities for the levels v′ = 3, 4, and 5. In contrast, no significant isotope effect could be observed for the other states of N(2)(+) identified in the photoelectron spectrum. For both (14)N(2)(+) and (15)N(2)(+) isotopologues all vibrational levels of these other states decay to an extent of at least 95% by predissociation.