The electronic structure of small fullerenes determined experimentally by anion photoelectron spectroscopy is compared with calculations. A huge mass signal and a large gap of 1.3 eV comparable to the gap of C 70 have been found for C 32 , indicating that this cluster is the most stable fullerene below C 60. Also C 36 , C 44 , and C 50 exhibit large gaps and surprisingly high stabilities. The criteria for the selection of clusters sufficientl stable to form a cluster material are discussed.

Photoelectron spectra of mass-separated Nb n Ϫ clusters reveal an even/odd alternation for nϭ6-17, indicating a closed electronic shell of the neutral even-numbered clusters. The HOMO-LUMO gap of Nb 8 , Nb 10 , and Nb 16 is found to be larger than that of the other even-numbered clusters, which correlates with the low H 2 reactivities of these species. The spectrum of Nb 15 Ϫ is different from all other clusters in this size range, which might be an indication for a geometric bcc shell closing. The influen e of the electronic structure of the clusters on the reactivity is discussed.

Photoelectron spectroscopy measurements and density functional theory calculations are combined to determine structures of Nb 2 n (n 3 8) clusters. A detailed comparison between observed and calculated electronic binding energies shows that the clusters have low-symmetry compact 3D structures and the lowest possible total spin, except for the three-and five-ato clusters which are in triplet states. We fin evidence for the coexistence of two isomers of Nb 2 8 under some experimental conditions. This approach shows great promise for structural characterization of small clusters.

Photoelectron spectra of metal-attached carbon cluster anions MC (M5Sc, Y, and La, 5#n#20) generated in a n laser-vaporization ion source were measured using a magnetic bottle time-of-fligh 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 2 vDE of the linear and monocyclic ring forms of C. It was found that PES features of MC (5#n#20, n5odd) could be n n 2 understood under the assumption that the p electronic structure of MC is similar to those of the linear carbon chains. n 2 However, the PES features of MC (12#n#20, n5even) indicate the presence of a p electronic structure similar to the n 2 isomers having ring form. Further possible electronic and molecular structures are presented and discussed for MC of odd n n and even n, respectively.

Mass spectra of LaC − n were taken by using a laser-vaporization source (LVS) and pulsed arc cluster ion source (PACIS) applied to La-carbon composite rods (1:130 atomic ratio). The mass spectrum using the LVS with annealing procedure has shown several magic numbers for LaC − n (n = 44, 50, 60, and 70), whereas only small LaC − n (up to n = 14) have been observed in the mass spectrum using the PACIS. Photoelectron spectra of some of these have been measured using a magnetic-bottle type time-of-flight electron spectrometer. These results indicate the exsistence of a few conformational isomers for small La-containing carbon cluster negative ions LaC − n (n = 5-8).