Dissociation energies of GdO, HoO, ErO, TmO, and LuO; correlation of results for the lanthanide monoxide series

High temperature gaseous reaction equilibria involving GdO, HoO, ErO, TmO, LuO, and certain reference oxides have been studied by mass spectrometry, using a molecular effusion beam source. From the reaction thermochemistry, the dissociation energies, D⁰₀, were derived as 169.5±3 kcal/mol (GdO), 144.1±3 kcal/mol (HoO), 143.9±3 kcal/mol (ErO), 121.8±3 kcal/mol (TmO), and 159.4±2 kcal/mol (LuO). Some of these values differ substantially from previous determinations. However, the new results together with several recent determinations and re‐evaluations yield a consistent set of results for the entire series from LaO to LuO. Trends in D⁰₀ values across the series can be correlated remarkably well with changes in the 4fⁿ6s²→4fⁿ⁻¹5d6s² electronic promotion energies in the gaseous metal atoms. Various aspects of the bonding are discussed.