LOW-ENERGY COLLISION-INDUCED DISSOCIATION AND PHOTODISSOCIATION STUDIES OF THE (N2O,H2O)(+) CLUSTER ION

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 t hermal and supersonic jet sources, and with both Ne and Ar as collisio n gases. In all experiments, H2O+, N2O+, and N2OH+ fragments are obser ved, 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 experime ntal thresholds are consistent with all fragment ions originating from a single isomeric precursor ion, [N2O . H2O](+). Whereas both N2O+ an d 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 fluster-ion isomeric forms produced in the jet sourer experiment. In the photodissociation experiments, branching ratios measured with the present jet source are very similar to those observed in previously re ported thermal experiments [S. T. Graul, H-S, Kim, and M. T. Bowers, i nt. J. Mass Spectrom, Ion Proc, 117, 507 (1992)]. All of the fragment ions can be accounted for by invoking an optical transition from groun d state [N2O . H2O](+) to an excited state associated with the N2O+H2O + ((A) over tilde) dissociation limit. The H2O+ and N2O+ branching rat ios are primarily governed by predissociation of the upper state follo wed by charge-transfer dynamics along a repulsive dissociation coordin ate. 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. (C) 1997 American Institute of Phy sics.