Experimental determination of heats of formation of negative ions and electron affinities of several boron and aluminium fluorides

Abstract

Thermodynamic properties for the negative ions of boron and aluminium fluorides were obtained by means of the effusion-mass spectrometric method over the temperature range 1100 to 1900 K. Studies were conducted involving negative ions with neutral molecules for the isomolecular reactions BF^–₂(g)+ F(g)→BF₂(g)+ F^–(g), BF₃(g)+ BF^–₂(g)→BF(g)+ BF^–₄(g), AlF₂(g)+ F^–(g)→AlF^–₂(g)+ F(g) and 2AlF₂(g)+ AlF^–₂(g)→2AlF(g)+ AlF^–₄(g). The heats of formation, ΔH_f298, for the ions BF^–₂(g), AlF^–₂(g), AlF^–₄(g), and BF^–₄(g) obtained from the reaction thermodynamics were – 191.7 ± 3, – 232.1 ± 3, – 500 ± 3 and – 433 kcal mol^–1, respectively. The electron affinities for BF₂ and AlF₂ were 50.7 ± 3 and 53.1 ± 3 kcal mol^–1, respectively.