VIBRATIONAL AND ELECTRONIC-PROPERTIES OF NEUTRAL AND NEGATIVELY CHARGED C-20 CLUSTERS

We computed vibrational and electronic properties of the cage, bowl, a nd ring isomers of neutral and negatively charged C-20, within density -functional theory, using fully optimized local-density and gradient-c orrected geometries. Vibrational and electronic spectra exhibit distin ctive features, which could be used to identify a given isomer and its charge state in molecular beams or thin films. Notable changes are ob served in both the Raman and infrared spectra when going from the neut ral to the charged isomers. We also calculated vibrational entropies f rom harmonic frequencies. Our results indicate that, above a critical temperature, the ring isomer is always stabilized by entropic effects, irrespective of the theoretical model used to compute the internal en ergy. In particular, gradient-corrected functionals predict both the n eutral and charged ring to be the most stable isomer at all temperatur es. Molecular-dynamics simulations were performed to study the geometr y of the ring at high temperature. Furthermore, we rationalized photoe lectron spectra of C-2n clusters, n=9-12, in terms of differences In t he electronic structure For even and odd n.