Low energy collision-induced dissociation and photodissociation studies of the (N2O,H2O)+ cluster ion

Abstract

Low energy collision-induced dissociation (CID) and photodissociation measurements of monohydrated nitrous oxide cluster ions are presented. The CID measurements have been conducted with ions produced in both thermal and supersonic jet sources, and with both Ne and Ar as collision gases. In all experiments, H2O+, N2O+, and N2OH+ fragments are observed, for which CID thresholds (0 K) of 1.04±0.06, 1.43±0.12 and 1.32±0.10 eV are determined, respectively. The thermal source experimental thresholds are consistent with all fragment ions originating from a single isomeric precursor ion, [N2O⋅H2O]+. Whereas both N2O+ and N2OH+ CID curves are comparable in the thermal source and supersonic jet source experiments, considerable differences are observed in the H2O+ CID measurements. The differences are attributed to loosely bound cluster-ion isomeric forms produced in the jet source experiment. In the photodissociation experiments, branching ratios measured with the present jet source are very similar to those observed in previously reported thermal experiments [S. T. Graul, H-S. Kim, and M. T. Bowers, Int. J. Mass Spectrom. Ion Proc. 117, 507 (1992)]. All of the fragment ions can be accounted for by invoking an optical transition from ground state [N2O⋅H2O]+ to an excited state associated with the N2O+H2O+ (Ã) dissociation limit. The H2O+ and N2O+ branching ratios are primarily governed by predissociation of the upper state followed by charge-transfer dynamics along a repulsive dissociation coordinate. Formation of N2OH+ is postulated to be controlled by a competing internal conversion process that leads to a longer-lived complex that decays to proton transfer products.