The standard molar atomization enthalpy and the standard molar enthalpy of formation of gaseous Si 2N from high-temperature mass spectrometry

A high-temperature mass-spectrometric study of the vaporization of (silicon + boron nitride) from a boron-nitride Knudsen cell was conducted in the temperature range T= 1688 K to 1921 K. The partial pressures of Si(g), Si 2(g), N 2(g), and Si 2N(g) were determined. The dissociation reaction: Si 2N(g) = 2Si(g) + 0.5N 2(g) was evaluated by using new thermal functions for Si 2N(g) calculated from the results of recent theoretical and experimental studies, and Δ r H ∘ mvalues: (538.0 ± 12.4) kJ· mol −1at T→ 0, and (545.1 ± 12.4) kJ·mol −1at T= 298.15 K were deduced by third-law evaluation. These values, in combination with the molar dissociation enthalpy of N 2(g) yielded the molar atomization enthalpies: Δ at H ∘ m(Si 2N,g) = (1008.8 ± 12.4) kJ·mol −1at T→ 0, and (1017.8 ± 12.4) kJ·mol −1at T= 298.15 K, and in combination with the standard molar enthalpy of formation of Si(g) yielded: Δ f H ∘ m(Si 2N,g) = (354.0 ± 14.8) kJ·mol −1at T→ 0, and (355.6 ± 14.8) kJ·mol −1at T= 298.15 K.