PHOTODISSOCIATION OF NIOBIUM - CARBON CLUSTERS AND NANOCRYSTALS

Metal compound clusters containing niobium and carbon are produced in a laser vaporization pulsed-nozzle cluster source. The mass distributi ons of cations produced from this source are measured under different conditions. These cations are mass-selected in a specially designed re flectron time-of-flight mass spectrometer and photodissociated at vari ous laser wavelengths. Mass distributions provide evidence for the pre ferential formation of the M(g)C(12) stoichiometry observed previously and associated with the ''met-cars'' cage structure. Additional abund ant masses indicate the formation of face-centered-cubic crystallite s toichiometries. Photodissociation in both the met-cars and crystallite systems results in the formation of a broad distribution of fragment ions, with some enhancement in abundance for the smaller symmetric cry stallites. This photochemistry is markedly different from that observe d previously for metal-carbon clusters containing titanium, vanadium, molybdenum, or zirconium.