Photoelectron spectroscopy study of MCn- (M=Sc, Y, and La, 5<=n<=20)

Photoelectron spectra of metal-attached carbon cluster anions MCn− (M=Sc, Y, and La, 5≤n≤20) generated in a laser-vaporization ion source were measured using a magnetic bottle time-of-flight photoelectron spectrometer with 6.4 eV photon energy. The vertical detachment energy (vDE) of each species was estimated from the spectra and compared with the vDE of the linear and monocyclic ring forms of Cn. It was found that PES features of MCn− (5≤n≤20, n=odd) could be understood under the assumption that the π electronic structure of MCn− is similar to those of the linear carbon chains. However, the PES features of MCn− (12≤n≤20, n=even) indicate the presence of a π electronic structure similar to the isomers having ring form. Further possible electronic and molecular structures are presented and discussed for MCn− of odd n and even n, respectively