N-O VERSUS N-N BOND ACTIVATION IN REACTION OF N2O WITH CARBON CLUSTERIONS - EXPERIMENTAL AND AB-INITIO STUDIES OF THE EFFECTS OF GEOMETRICAND ELECTRONIC-STRUCTURE

We report a combined experimental and theoretical study of the reactio n of small carbon cluster cations with N2O aimed at understanding the reaction mechanism and how it is affected by the electronic and geomet ric structure of the C-n(+) reactants. Cross sections for reaction of C-n(+) (n=3-12) with N2O were measured over a collision energy range f rom 0.1-10 eV, using a guided ion beam tandem mass spectrometer. Ab in itio calculations were used to examine the structure and energetics of reactant and product species. Small clusters, which are linear, react with no activation barrier, resulting in either oxide or nitride form ation. The branching between oxide and nitride channels shows a strong even-odd alternation, with even clusters preferentially forming nitri des. This appears to be correlated with an even/odd alternation in the ionization potential of the CnN. The larger, monocyclic C-n(+) have a ctivation barriers for reaction, and a completely different product di stribution. Secondary reactions of the primary oxide and nitride produ cts were studied at high N2O pressures. Products containing two O or t wo N atoms are not observed, but it is possible to add one of each. Po ssible reaction mechanisms are discussed and supported by thermochemis try derived from spin restricted ab initio calculations.