Photoionization efficiency data for (CO2)+2–4 and (N2O)+2 in the region 600–1020 Å have been obtained using the molecular beam method. The ionization energies (I.E.) of (CO2)2, (CO2)3, (CO2)4, and (N2O)2 were measured to be 13.32±0.02 eV (930.5±1.5 Å), 13.24±0.02 eV (936.5±1.5 Å), 13.18±0.02 eV (941±1.5 Å), and 12.35±0.02 eV (1004±1.5 Å), respectively. Using these values, the known I.E.’s for CO2 and N2O, and the estimated binding energies for (CO2)2 and (N2O)2, the dissociation energies for CO+2⋅CO2, (CO2)+2⋅CO2, (CO2)+3⋅CO2, and N2O+⋅N2O were deduced to be 11.8±1.0, 3.3±1.4, 2.8±1.4, and 13.1±0.9 kcal/mol, respectively. The ion–molecule half reaction N2O+⋅N2O→N3O+2+N was observed. The analysis of the photoionization efficiency curves for (CO2)+2 and (N2O)+2 suggests electronic predissociation or direct dissociation might be important dissociation mechanisms for the CO*2(n)⋅CO2 and N2O*(n)⋅N2O excited Rydberg dimers.

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