GAS-PHASE THERMOCHEMISTRY OF THE GROUP-3 DIOXIDES - SCO2, YO2 AND LAO2

Gas-phase ScO2, YO2, LaO2 and the singly charged cations of these species are formed in endothermic reactions between MO+ (M = Sc, Y, and La) and NO2 in a guided ion beam mass spectrometer. The cross sections of these reactions are measured as a function of kinetic energy and are interpreted to give the following 0 K bond energies (in eV): D0(OSc-O) = 3.95 +/- 0.33, D0(OY-O) = 4.14 +/- 0.22, D0(OLa-O) = 4.20 +/- 0.33, D0(OSc+-O) = 1.72 +/- 0.19, D0(OY+-O) = 1.76 +/- 0.16, and D0(OLa+-O) = 0.99 +/- 0.3l. Values for the MO2 ionization energies (in eV) are determined to be IE(SCO2) = 8.66 +/- 0.20, IE(YO2) = 8.23 +/- 0.16 and IE(LaO2) = 8.11 +/- 0.35. The differences between these values and estimates in the literature are discussed by considering the nature of the bonding in MO2 and MO2+.