COMPLEX ELECTRON-AFFINITY PROCESSES IN CLUSTERS OF S AND SI

Vertical and in some cases adiabatic electron affinities are calculated for the clusters S4 and Si(n), n = 3 - 7 with large basis sets. The effects of electron correlation are taken into account by Cl and Green function techniques. The clusters show a complex behaviour upon electron attachment. The isomers Of S4 show normal electron capture processes as well as electron attachment with shake-up. The Si clusters show multiple affinity states resulting from capture of an electron into different orbitals: Si3 C2v has at least three, Si4 D2h four, Si5 D3h two, Si5 D4v one, Si6 C2v three and Si7 D5h two affinity states (vertical processes: Si(n) + e- --> Si(n)- + hv). For the Si(n) clusters in some cases shake-up affinities are calculated which are positive. The effects of electron correlation on the electron affinities are extremely large for the Si clusters in particular. In several cases the differences between the adiabatic and vertical electron afrinities are very large amounting up to 1.5 eV.