The dynamics of photodissociation of the gas phase N 2O·H 2O) + cluster ion

Abstract

The photodissociation dynamics of the positive cluster ion of N 2O and H 2O have been examined for the wavelength range 657–458 nm (1.89–2.71 eV). The major products at all wavelengths are N 2O + H 2O, which are formed by excitation to a repulsive upper surface followed by rapid dissociation. The next most abundant products are H 2O + N 2O, 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 H 2O + + N 2O, possibly involving a bound excited state. A minor N 2OH + + 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 N 2O + · H 2O and is a logical precursor for the N 2O +/H 2O products and the major portion of the H 2O +/N 2O products that is formed by a repulsive dissociation mechanism. The second isomer is N 2OH +·OH, probably the precursor for the N 2OH +/OH products and perhaps a minor portion of the H 2O +/N 2O products observed from excitation at 657 nm. Phase space modeling of the N 2OH + kinetic energy release distribution suggests a binding energy of about 1.2 eV for the N 2OH +·OH cluster. The relative binding energy from ab initio calculations suggests that the N 2O +/H 2O cluster is bound by about 0.5 eV. Mechanisms for formation of the observed photofragments are proposed.