A b i n i t i o MRD CI investigation of the optical spectra of C4 and C5 clusters

Abstract

The ground and excited electronic states of linear and rhombic C4 and linear C5 clusters have been studied with ab initio single reference and multireference configuration interaction calculations. The spectrum of linear C4 is characterized by the existence of low-lying Π states at 1–1.5 eV above the 3Σ−g ground state. In rhombic C4, which has very similar ground state energy as the linear form, the first allowed transition is found at 2.4 eV. The optical spectrum of linear C5 exhibits some similarities with that of linear C3: in both molecules the ground state is 1Σ+g and the lowest allowed transition, 1Πu←1Σ+g, is about 3 eV above the ground state.