Determination of dissociation energies for some alkaline earth (hydro-) oxides in CO/N2O flames

Abstract

The formation of mono-oxides and mono-hydroxides of the alkaline earth metals calcium, strontium, and barium is investigated by a flame spectrometric method. By comparison of the atomic resonance line intensities of sodium and of the alkaline earth metals mentioned, the ratio of the total molecular compound concentration to the free atomic metal concentration is measured in two CO/N2O flames with varying water input. Dihydroxide molecules appear to be of minor importance in our flames based on published dissociation energies for these species, and the atom to total molecule ratio is corrected for their presence by calculation. From the resulting relative oxide plus monohydroxide concentrations, dissociation energies for these compounds are determined with a trial-and-error method by third-law calculations. The resulting energies are compared with literature values, and ``best values'' are given. These are Do(CaO) = 3.75 ± 0.20 eV, Do(SrO) = 4.06 ± 0.10 eV, Do(BaO) = 5.30 ± 0.10 eV, Do(CaOH) = 4.44 ± 0.10 eV, Do(SrOH) = 4.38 ± 0.10 eV, and Do(BaOH) = 4.88 ± 0.06 eV. The electronic partition functions for the oxide molecules are assumed to be 3, 3, and 6, respectively.