APPEARANCE ENERGIES OF SMALL CLUSTER IONS AND THEIR FRAGMENTS

Appearance energies of the cluster ions (CO2)n+ (2 less-than-or-equal- to n less-than-or-equal-to 4), (N2,O)n+ (2 less-than-or-equal-to n les s-than-or-equal-to 4) and (NH3)(n)NH4+ (0 less-than-or-equal-to n less -than-or-equal-to 7), and the cluster ion fragments (N2) . O)+ and (N2 O . NO)+ have been determined by electron impact ionization of neutral clusters formed in a supersonic molecular beam. Results obtained for CO2)n+ (2 less-than-or-equal-to n less-than-or-equal-to 4), (N2O)n+ (2 less-than-or-equal-to n less-than-or-equal-to 4), (N2O . NO)+ and (NH 3)(n)NH4+ (0 less-than-or-equal-to n less-than-or-equal-to 2) are in g eneral agreement with previously reported appearance energies for thes e species, while the appearance energies of (N2O . O)+ and (NH3)(n)NH4 + (3 less-than-or-equal-to n less-than-or-equal-to 7) have been measur ed for the first time. Binding energies deduced from appearance energy measurements for the (CO2)2+, (CO2)3+ and (N2O)2+ cluster ions are ob served to be in accord with results obtained using ion-molecule equili briuM methods. Possible mechanisms for the formation of the cluster fr agment ions (N2) . O)+ and (N2O . NO)+ are discussed.