Theoretical Study of the Heats of Formation of Small Silicon-Containing Compounds

Heats of formation for nine small silicon-containing molecules were obtained from large basis set ab initio calculations using coupled cluster theory with a perturbative treatment of triple excitations. After adjusting the atomization energies for the finite basis set truncation error, core/valence correlation, scalar relativistic, higher order correlation, and atomic spin−orbit effects, the theoretical and experimental 0 K values of Δ H f values were in good agreement. Using 106.6 kcal/mol as the heat of formation of silicon, we obtain Δ H f values of SiH = 87.7 ± 0.4 vs 89.5 ± 0.7 (expt); SiH 2 ( 1 A 1 ) = 64.1 ± 0.4 vs 65.5 ± 0.7 (expt); SiH 2 ( 3 B 1 ) = 85.4 ± 0.4 vs 86.5 ± 0.7 (expt); SiH 3 = 47.3 ± 0.5 vs 47.7 ± 1.2 (expt); SiH 4 = 8.7 ± 0.6 vs 9.5 ± 0.5 (expt); Si 2 = 138.8 ± 0.4 vs 139.2 (expt); Si 2 H 6 = 19.7 ± 0.5 vs 20.9 ± 0.3 (expt); SiF = −14.8 ± 0.4 vs −5.2 ± 3 (expt); SiF 2 = −151.7 ± 0.5 vs −140.3 ± 3 (expt); and SiF 4 = −384.5 ± 0.9 vs −384.9 ± 0.2 (expt). Based on the present work, we suggest a number of revisions in the interpretation of the experimental data. Although a revision in Δ H f °(Si) to 107.4 ± 0.6 kcal/mol at 0 K leads to improved agreement between theory and experiment for the Si x H y compounds, it worsens agreement for SiF 4 . Given the remaining uncertainties in the theoretical approach, more definitive conclusions do not appear to be warranted.