Mass spectrometric studies of gaseous ThO and ThO2

High temperature mass spectrometric techniques have been used to study the equilibria (1/2)Th(s)+(1/2)ThO₂(s)=ThO(g), (1); ThO(g)+Si(g)=Th(g)+SiO(g), (2); Th(g)+ThO₂(g)=2 ThO(g), (3). From the equilibrium data and related electron impact measurements the following quantities have been derived: Δ _fH(ThO,g,298.15 K) =−4.6±5.9 kJ/mol; $D_0\mathrm{°\hspace{0.17em}(}\mathrm{ThO}\text{)=848± 13\hspace{0.17em}}\mathrm{kJ}/\mathrm{mol}$ (or 8.78 ±0.13 eV); IP(ThO) ≥6.0 eV; Δ _fH(ThO₂,g, 298.15 K)=−443±25 kJ/mol; $D_0\mathrm{°(}{\mathrm{ThO}}_2\text{)1532± 30\hspace{0.17em}}\mathrm{kJ}/\mathrm{mol}$ (or 15.9±0.3 eV); and IP(ThO₂)=8±1 eV. A second‐law analysis of Reaction (1) gives a measure of the magnitude of the electronic partition function of ThO. Difficulties in interpreting the ThO ionization threshold are described. The relationship of these measurements to recent kinetic studies is briefly discussed.