Mass spectra and vapor pressure of scandium triiodide, and thermochemistry for the dimerization of ScI 3 (g)

Abstract

Mass spectrometry and Knudsen cell vapor pressure measurements have been made to study the equilibrium vapor over ScI 3 (c). A significant Sc 2I 6(g) concentration is present in the vapor in the Knudsen cell temperature range. The enthalpy and entropy of dimerization are −49 kcal mol −1 and −43 cal mol −1 deg −1, respectively. From the vapor pressures and the equilibrium constants for the dimerization, the following thermodynamic properties have been derived at 298 K: for ScI 3(c), ΔH f o = −132 kcal mol −1, ΔH s o = 64.8 kcal mol −1, S o = 47.2 cal mol −1 deg −1; for ScI 3(g), ΔH f o = −66 kcal mol −1, S o = 103.3 cal mol −1 deg −1; for Sc 2I 6(g), ΔH f o = −181 kcal mol −1, S o = 164.0 cal mol −1 deg −1.