ELECTRON-AFFINITIES AND SINGLET-TRIPLET (DOUBLE-QUARTET) SPLITTINGS OF SMALL UNSATURATED SILICON HYDRIDE SYSTEMS

The singlet-triplet (Delta E(ST)) and doublet-quartet (Delta E(DQ)) sp littings and electron affinities (EA) of various silicon hydrides and substituted species were calculated. Electropositive substituents (Li and SiH3) favour the high-spin states, others (CH3 and F) the low-spin states. EA values are increased by silyl and decreased by methyl subs tituents. The Delta E(DQ) values are -0.57, 0.92, 1.68 and 3.63 eV for SiLi, SiSiH3, SiCH3 and SiF, respectively. The corresponding EA value s are 0.88, 1.32, 0.65 and 0.76 eV, respectively. CH2-SiH3, SiH2-CH3 a nd SiH2-SiH3 have EAs of 0.39, 0.79 and 1.46 eV. Si2H is found to have several minima on the doublet and quartet energy surfaces. The smalle st Delta E(DQ) is 1.1 eV, similar to the value of 1.35 eV of Si2H3. Bo th species have electron affinities > 2 eV. The disilene anion (Si2H4- ) was considered, particularly with regard to its stability to rotatio nal isomerization.