Ab initio calculation of anharmonic force fields for the methyl, silyl, germyl, and stannyl halides

Theoretical anharmonic force fields are reported for 16 symmetric tops MH3X (M=C, Si, Ge, Sn; X=F, Cl, Br, I). All molecules are treated uniformly at the Hartree-Fock level using effective core potentials and polarized double-zeta basis sets for the valence electrons. The calculated vibration-rotation interaction constants, l-doubling constants, ground-state rotational constants, sextic centrifugal distortion constants, anharmonicity constants and anharmonic resonance parameters are compared with the available experimental data. The agreement is generally satisfactory, except when there are complications due to resonances. Many spectroscopic constants are predicted which have not been measured, including those for the unknown SnH3F molecule