Isomers of niobium clusters: Direct spectroscopic evidence

We have reproduced kinetics results indicating that niobium clusters in the size range Nb9–Nb12 are produced in two isomeric forms which possess widely different rates reactivity toward D2. We have exploited this difference in reactivity to record photoionization efficiency spectra of the unreactive forms of Nb9, Nb10, and Nb12 as well of a mixture containing predominantly the reactive forms. We find that the photoionization thresholds measured for Nb9 and Nb12 with the reactive forms of these species depleted via reaction with D2 are shifted to higher energies compared those recorded without D2 present. The photoionization threshold energies for both unreactive and reactive forms of Nb10 are approximately equal.