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

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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.
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