THE DYNAMICS OF PHOTODISSOCIATION OF THE GAS-PHASE (N2O.H2O)+ CLUSTER ION

The photodissociation dynamics of the positive cluster ion of N2O and H2O have been examined for the wavelength range 657-458 nm (1.89-2.71 eV). The major products at all wavelengths are N2O+ + H2O, which are formed by excitation to a repulsive upper surface followed by rapid dissociation. The next most abundant products are H2O+ + N2O, which are formed predominantly by rapid dissociation from a repulsive surface. At the longest wavelength (657 nm), there is evidence for a second mechanism for production of H2O+ + N2O, possibly involving a bound excited state. A minor N2OH+ + OH channel is observed at all wavelengths, and arises by vibrational predissociation in the ground state after photoexcitation to a bound excited state. Molecular orbital calculations indicate that at least two isomers of the cluster ion exist on the ground state potential energy surface. One isomer is best represented as N2O+ .H2O and is a logical precursor for the N2O+/H2O products and the major portion of the H2O+/N2O products that is formed by a repulsive dissociation mechanism. The second isomer is N2OH+ .OH, probably the precursor for the N2OH+/OH products and perhaps a minor portion of the H2O+/N2O products observed from excitation at 657 nm. Phase space modeling of the N2OH+ kinetic energy release distribution suggests a binding energy of about 1.2 eV for the N2OH+ .OH cluster. The relative binding energy from ab initio calculations suggests that the N2O+/H2O cluster is bound by about 0.5 eV. Mechanisms for formation of the observed photofragments are proposed.