The dissociation energy of gaseous ZrO,D0deg; (ZrO), and the heat of atomization of gaseous ZrO2have been measured using a high temperature mass spectrometer. A number of equilibria were studied and the following results were derived: Dgr;fH(ZrO,g,298.15 K) =83plusmn;12 kJ/mol,D0deg; (ZrO) =761plusmn;15 kJ/mol) (or 7.89plusmn;0.15 eV), Dgr;fH(ZrO2,g,298.15K) =minus;298plusmn;30 kJ/mol, andD0deg; (ZrO2) =1386plusmn;30 kJ/mol (or 14.4plusmn;0.3 eV). The ionization potentials of ZrO and ZrO2were derived from the measured appearance potentials. In the case of ZrO it was necessary to make corrections for the thermal populations of lowhyphen;lying electronic states. The derived values are I.P.(ZrO) =6.0plusmn;0.2 eV, I.P.(ZrO2) =9.4plusmn;0.2 eV. These measurements are discussed in relation to other studies. Uncertainties in the derived thermochemical quantities owing to uncertainties in the spectral data are discussed. The chemical bonds in ZrO and ZrO2are briefly discussed.
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