Thermochemical properties of gaseous ZrO and ZrO2

The dissociation energy of gaseous ZrO, D00(ZrO), and the heat of atomization of gaseous ZrO2 have been measured using a high temperature mass spectrometer. A number of equilibria were studied and the following results were derived: Δ/sub f/H (ZrO,g,298.15 K) = 83 +- 12 KJ/mol, D00(ZrO) = 761 +- 15 KJ/mol) (or 7.89 +- 0.15 eV), Δ/sub f/H(ZrO2,g,298.15 K) = -298 +- 30 KJ/mol, and D00(ZrO2) = 1386 +- 30 kJ/mol (or 14.4 +- 0.3 eV). The ionization potentials of ZrO and ZrO2 were derived from the measured appearance potentials. In the case of ZrO it was necessary to make corrections for the thermal populations of low-lying electronic states. The derived values are I. P. (ZrO) = 6.0 +- 0.2 eV, I. P. (ZrO2) = 9.4 +- 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 ZrO2 are briefly discussed