A b i n i t i o calculations of transition probabilities and potential curves of SiH

The complete active space SCF (CASSCF) method has been used to calculate the SiH A 2Δ–X 2Π electronic transition moment curve. The radiative lifetime deduced for v′=0 on basis of this transition moment curve and averaged over a number of rotational levels was 508 ns, which is in very good agreement with experimental results. The contracted CI (CCI) method was used to obtain the electronic potential functions of the A 2Δ and X 2Π states and the ground state electric dipole moment function. The dipole moment calculated at the equilibrium geometry (re=1.520 Å), μe=0.123 D, is in excellent agreement with previous theoretical results. The ground state dissociation energies of SiH and CH were calculated with comparable basis sets in order to resolve a discrepancy regarding the SiH dissociation energy which prevails in the literature. The calculated dissociation energy D0(SiH)=3.00 supports the value obtained from observation of a predissociation in the B 2∑+ state of SiH, D0≤3.06 eV. Very recently this upper bound to the SiH dissociation energy also found support from a photoelectron spectroscopy experiment. The previously observed predissociation in the A 2Δ state, which suggested a 10% higher dissociation energy, is discussed in some detail and it is shown that the prior interpretation of this predissociation as an interaction between the A state and the ground state continuum is reasonable, but only yields an upper limit to the dissociation energy.