Dissociation energies of CaI, SrI, and BaI from high temperature mass spectrometry

Abstract

Equilibrium effusion beams containing the gaseous molecules CaI, SrI, and BaI were generated by the reaction of HI with the corresponding metal oxides at 1500 to 1900 K. Beam composition data obtained by mass spectrometry were used to determine the equilibrium constants of gaseous reactions involving the monoiodides and certain reference molecules. Reaction enthalpies then were evaluated by second and third law methods, from which the dissociation energies D₀° (Cal) =62.1±2.5, D₀° (SrI) =63.6±1.4, and D₀° (BaI) =71.4±1.0 kcal/mole were derived. The results are consistent with data obtained earlier for the diatomic metal fluorides, chlorides, and bromides, and they are compatible with the predictions of the Rittner polarizable‐ion model. Various features of the chemical bonding are discussed. A correlation of the thermochemical properties across the entire halide series allows one to estimate reliable dissociation energies for BeBr, BeI, MgBr, and MgI.