CONFIGURATION-INTERACTION CALCULATIONS OF THE VERTICAL ELECTRONIC-SPECTRUM OF SILANE

Ab initio multireference single- and double-excitation configuration interaction (MRD-CI) calculations are reported for a large series of the lowest-lying electronic states of silane SiH4. The transition energies computed with and without the multi-reference Davidson correction are found to agree within 0.2 eV, which is an indication that the full CI level for the AO basis employed is approached to this degree of accuracy. These results are found to be in good agreement with the CIPSI values reported earlier by Larrieu et al., but lie as much as 1.0-1.5 eV above their Davidson-corrected MRSD-CI transition energies. On this basis it is argued that both the spectral peaks observed at 8.99 and 9.67 eV should be assigned as 2t2-->4s transitions, whereby the observed splitting is caused by a Jahn-Teller distortion of the upper 1T2 state. Optical f values are also reported, as well as computed singlet-triplet splittings. Finally the SiH4 dissociation process into SiH2 and H-2 products is also investigated.