Electron affinities, shake-up affinities, and ionization energies of S4 isomers

Nine isomers of S4 (D∞h,D2h,D4h,D3h,D2i,C2v, C2h,C3v,Cs) have been studied with large basis sets in Green function, CASSCF, and single and multi reference CI approaches. The C2v and D2h isomers are found to be nearly equally stable with the C2v isomer 1 kcal/mol below the D2h form and the C2h isomer about 10 kcal/mol higher in energy. All isomers have an appreciable electron affinity and some have several bound negative ion states. Besides normal electron affinities they have shake-up affinities, which may also be strongly positive. The lowest ionization energies of the isomers range from 7.5 to 9 eV.