Ab initio quantum mechanical methods, including the self-consistent field (SCF), single- and double-excitation configuration interaction (CISD), single- and double-excitation coupled cluster (CCSD), and the single-, double-, and perturbative triple-excitation coupled cluster [CCSD(T)] have been applied to three stationary points on the SiH7+ potential energy hypersurface. Double-ζ plus polarization (DZP) and triple-ζ plus double-polarization [TZ2P and TZ2P(f,d)] basis sets were employed. The C2 structure, where two symmetry-equivalent H2 subunits complex the SiH3+ cation, was found to be the global minimum, in agreement with the findings of Liu and Zhou (J. Phys. Chem. 1993, 97, 9555). The bound vs free H2 harmonic vibrational frequency shift obtained at the TZ2P CCSD level (259 cm-1) is 36 cm-1 less than the experimental frequency shift (295 cm-1), compared with the shift obtained by Liu and Zhou with second-order perturbation theory, which was 33 cm-1 higher than the value from experiment. The theoretical rotational constants are compared with the experiments of Okumura's group. The dissociation energy D0 of SiH7+ to yield SiH5+ and H2 is sizable, 4.6 kcal/mol [TZ2P(f,d)] CCSD-(T) + ZPVE(TZ2P CCSD)], much larger than the analogous value for CH7+.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry