Isotope Effects in the Predissociation of Excited States of N Produced by Photoionization of N and N 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 N-14(2) or N-15(2) as photoionization target. The results confirm that predissociation of the C-2 Sigma(+)(u) state of N-14(2)+ is faster than emission to the electronic ground-state by a factor 10 or more for all vibrational levels v' >= 3, while for N-15(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 N-14(2)+ and N-15(2)+ isotopologues all vibrational levels of these other states decay to an extent of at least 95% by predissociation.