Determination of dissociation energies of alkaline-earth chlorides, bromides and hydroxides by flame photometry

Abstract

The ratio of the integral intensity of the bands MX and lines M, where M = Ca, Sr, Ba and X = Cl, Br, and OH, was measured in the spectra of 16 flames aH₂+bO₂+cN₂+dH₂O with additives of chlorine or bromine (T= 1810–2580 K). On the basis of these measurements it was found (in kcal mol^–1)D₀(CaCl)= 94.1±1.6; D₀(CaBr)= 75.7±5.4; D₀(Ca—OH)= 96±3, D₀(SrCl)= 95.6±1.8; D₀(SrBr)= 78.4±4.4; D₀(Sr—OH)= 95±3, D₀(BaCl)= 106.8±2.2; D₀(BaBr)= 87.5±2.2; D₀(Ba—OH)= 111±4.

The ratio of an atomic line intensity of M in the spectrum of flame without halogen to its intensity in the presence of halogen was investigated. The data obtained indicate that in the flame, besides the monohalogenide and dihalogenide, there is formed at least one metallic compound which contains 1 atom of halogen, apparently MXOH. The approximate values of the bonding energies in the molecules MCl₂, MBr₂, MClOH and MBrOH were determined.