Ab initio calculation of harmonic force fields and vibrational spectra for the methyl, silyl, germyl, and stannyl halides

Theoretical harmonic force fields are reported for 16 symmetric tops H3MX (M=C, Si, Ge, Sn; X=F, Cl, Br, I). Based on the evaluation of systematic test calculations for H3CF, H3CCl, H3SiF, and H3SiCl, all molecules are treated uniformly at the Hartree–Fock level using effective core potentials and polarized double‐zeta basis sets for the valence electrons. For each molecule the calculated geometries, rotational constants, frequencies, centrifugal distortion constants, Coriolis coupling constants, and infrared band intensities are compared with the available experimental data. The agreement is satisfactory and generally of similar quality as in analogous all‐electron Hartree–Fock calculations of molecules with first‐row atoms. It is stressed that theory may reliably provide data which are hard to derive from experiment, e.g., the off‐diagonal symmetry force constants and the signs of the dipole moment derivatives. The effects of scaling the theoretical force fields are investigated carefully including the transferability of scaling factors between related molecules, and the vibrational spectrum of the as yet unknown H3SnF molecule is predicted. Our present results indicate that the chosen theoretical approach is generally suitable for studying the harmonic force fields of inorganic molecules with heavy main‐group elements