Mass spectrometric determination of the heats of formation of the silicon fluorides SiF(g), SiF2(g) and SiF3(g)

Abstract

An effusion-mass spectrometric study of the reaction of SiF₄(g) with Si(c, 1) in the temperature range 1590–1782 K has been completed. Second and third law reaction enthalpies were obtained for SiF₄(g)+ Si(g)= 2SiF₂(g), SiF₄(g)+ SiF₂(g)= 2SiF₃(g), and SiF₂(g)+ Si(g)= 2SiF(g). From the heats of reaction third law ΔH_f298 values of –5.8 ± 0.5, –140.6 ± 0.3 and –259.3 ± 0.5 kcal mol^–1 were obtained for SiF(g), SiF₂(g) and SiF₃(g), respectively. For the dissociation of SiF(g)→(³P₀)Si(g)+(²P)F(g) a third law dissociation energy value of 131.2 ± 0.5 kcal mol^–1 was calculated.