Thermodynamic Properties of Gaseous Yttrium Monoxide. Correlation of Bonding in Group III Transition-Metal Monoxides

Abstract

The vapor from solid yttrium sesquioxide contained in a Knudsen cell made of tungsten has been investigated by measuring the absolute effusion rate and by studying the effusate in a mass spectrometer. The latter demonstrates that the gaseous species are yttrium monoxide, oxygen, and a small amount of yttrium. Measurements of the appearance potentials for the ions enable one to conclude that the ratio of monoxide‐to‐metal is at least 65 and that above 15 eV significant fragmentation of YO by the ionizing electrons to yield Y⁺ occurs. From the absolute effusion rates one derives the free energy of formation, $${\mathrm{\Delta F}}_f^{\circ }(\mathrm{YO},\mathrm{g}\text{)=−21 800–10.96\hspace{0.17em}T,}$$ and the dissociation energy, 7.31±0.10 eV, for gaseous yttrium monoxide. A correlation of the dissociation energies and the molecular parameters of the monoxides of Group III transition metals indicates that the unexpected increase in bonding with increasing radii is accompanied by an increase in the electronic entropy of the metal atom. The correlation demonstrates the role of excited atomic states in chemical bonding.