Dissociation Energy of Gaseous LaO

The gaseous species in thermodynamic equilibrium with La(l) — La2O3(s) mixtures in the temperature range 1650°K to 1900°K have been studied mass spectrometrically. The major ions observed were La+ and LaO+. These ions were shown to be formed predominantly from La(g) and LaO(g), respectively. A thermodynamic treatment of ion currents yields a value of ΔH00=100±4 kcal/g atom for the heat of vaporization of La(s) and a value of ΔH00=189±8 kcal/mole for the reaction LaO(g)=La(g)+O(g) or D0(LaO)=8.15±0.35 ev.