Laser studies of the reactivity of small niobium clusters with benzene

Using a laser vaporization flow reactor apparatus, small niobium clusters (Nb/sub x/, x = 1-15) are reacted with benzene and detected with an excimer laser (ArF) photoionization time-of-flight mass spectrometer. At low ionizing laser intensities, the probability of dehydrogenation of Nb/sub x/C/sub 6/H/sub 6/ clusters to Nb/sub x/C/sub 6/ is found to be a maximum for x = 5, 6 and 11 and a minimum for x < 4 as well as for clusters with 8 and 10 niobium atoms. As the ionizing laser intensity increases, it is possible to photochemically drive the dehydrogenation reaction of the x = 7, 9, 12, 13 clusters with one extra photon above ionization while the x = 8 and 10 clusters are found to require two photons above ionization. These results are discussed in terms of the stabilities of these clusters relative to their photochemical ionic products