Thermochemical properties of the gaseous alkaline earth monohydroxides

The dissociation energies D°0(Ca–OH), D°0(Sr–OH), and D°0(Ba–OH) were measured using high temperature mass spectrometry. By passing H2(g) over CaO(s), SrO(s), and BaO(s) in a Mo Knudsen cell, gas-phase equilibria involving CaO(g), CaOH(g), SrO(g), SrOH(g), BaO(g), and BaOH(g) were studied. These results yielded D°0(Ca–OH)≊D°0(Sr–OH) = 92±4 kcal/mol (4.0±0.17 eV) and D°0(Ba–OH) = 107±4 kcal/mol (4.55±0.17 ev). In addition, the following appearance potentials were measured: A.P.(MgOH+) = 7.5±0.3 eV, A.P.(CaOH+) = 5.55±0.2 eV, A.P.(SrOH+) = 5.1±0.2 eV, A.P.(BaOH+) = 4.35±0.3 eV, A.P.(CaO+) = 7.6±0.5 eV, A.P.(SrO+) = 7.0±0.2 eV, and A.P.(BaO+) = 6.8±0.2 eV. Other important properties, e.g., proton affinities and heats of formation, are derived from these measurements. Bonding in the alkaline earth monoxides and monohydroxides is discussed briefly.