Theoretical investigations of small multiply charged cations. I. SiH ²⁺

In excellent agreement with experiments, high levels ab initio MO calculations of the multireference CI (MRD-CI) and complete active space SCF (CASSCF) type show a deep potential well for the X²Σ ⁺ ground state of the diatomic SiH²⁺ dication with a barrier of 1.06 eV (CASSCF) and 1.07 eV (MRD-CI) for the charge separation reaction. This result, which is in distinct contrast to the findings for the valence isoelectronic CH²⁺ dication, is explained by the charge polarization character of the SIH²⁺ ground state. Also the first excited A ²Π state was found by MRD-CI to be weakly bound.