Mass Spectra of Aluminum(III) Halides and the Heats of Dissociation of Al2F6(g) and LiF·AlF3(g)

Abstract

Mass spectra of gaseous aluminum(III) chloride and bromide have been obtained and interpreted quanitatively in terms of the degree of association in the vapor phase. Ion currents indicative of a molecular trimer of AlCl₃ have been observed. Mass spectra of the vapors effusing from a Knudsen cell containing AlF₃ have been obtained and the stability of the molecular dimer of AlF₃(g) has been determined quantitatively. Mass spectra of vapors from LiF–AlF₃ mixtures indicate the existence of a stable LiF·AlF₃(g) molecule. Ion current data have been obtained as a function of condensed phase composition. A second complex molecular species which appears to be either (LiF)₂·AlF₃(g) or (LiF·AlF₃)₂(g) has been observed. For the reaction Al₂F₆(g)=2AlF₃(g), ΔH°₁₀₀₀=48.0±4.0 kcal/mole dimer, and for LiF·AlF₃(g)=LiF(g)+AlF₃(g), ΔH°₁₀₀₀=73±4 kcal/mole.