Anharmonic force field, vibrational energies, and barrier to inversion of SiH3-

The full quartic force field of the ground electronic state of the silyl an ion (SiH3-) has been determined at the CCSD(T)-R12 level employing a [Si/H] =[16s11p6d5f/7s5p4d] basis set. The vibrational energy levels, using the qu artic force field as a representation of the potential energy hypersurface around equilibrium, have been determined by vibrational perturbation theory carried out to second, fourth, and sixth order. The undetected vibrational fundamental for the umbrella mode, nu(2), is predicted to be 844 cm(-1). H igh-quality ab initio quantum chemical methods, including higher-order coup led cluster (CC) and many-body perturbation (MP) theory with basis sets ran ging from [Si/H] [5s4p2d/3s2p] to [8s7p6d5f4g3h/7s6p5d4f3g] have been emplo yed to obtain the best possible value for the inversion barrier of the sily l anion. The rarely quantified effects of one- and two-particle relativisti c terms, core correlation, and the diagonal Born-Oppenheimer correction (DB OC) have been included in the determination of the barrier for this model s ystem. The final electronic (vibrationless) extrapolated barrier height of this study is 8351 +/- 100 cm(-1). (C) 2000 American Institute of Physics. [S0021-9606(00)30308-7].