Anharmonic force fields and accurate thermochemistry of H2SiO, cis-HSiOH, and trans-HSiOH

The energetics, structure, and anharmonic force fields of the isomers H2SiO, cis-HSiOH, and trans-HSiOH have been studied using coupled cluster methods and basis sets of up to spdfgh quality;and including inner-shell correlation. Inner polarization functions on Si were found to be of crucial importance for the correct reproduction of computed properties. At the basis set limit at 0 K, the H2SiO isomer is more stable than the two others by about 0.5 kcal/mol. cis-HSiOH is marginally more stable than trans-HSiOH (0.05 kcal/mol); deuteration shifts the equilibrium toward the trans form. The computed fundamentals for the (H,D) and (O-16,O-18) isotopomers closely track the experimental ones in an argon matrix, except for a few reassignments which impose themselves. Our best computed geometry for H2SiO, r(SiH) 1.4733 Angstrom, r(SiO) = 1.5140 Angstrom, and theta(HSiH) = 111.97 degrees, agrees within experimental error with the most recent determination. Using a recently proposed Schwartz-type extrapolation, we obtain the following Sigma D-0 values (including core correlation, atomic spin-orbit splitting, and anharmonic zero-point energy): SiO 189.9, SiH2 (a B-3(1)) 124.5 kcal/mol, SiH2 (X (1)A(1)) 145.80 kcal/mol, and H2SiO 292.6 kcal/mol, which we expect to be accurate to about 0.3 kcal/mol. The former three agree with experiment to within the latter's uncertainty but have smaller error bars. As a byproduct, we obtain a basis set limit for the singlet-triplet splitting in silylene, T-0 = 21.35 +/- 0.1 kcal/mol. To assist future gas-phase infrared and microwave studies on silanone and hydroxysilylene, computed anharmonic spectroscopic constants for all species concerned have been presented, and complete anharmonic force fields are available as Supporting Information.