Vanadium clusters:: Reactivity with CO, NO, O2, D2, and N2

We have investigated the size-dependent reactivity of vanadium clusters, V-10-V-60, with CO, NO, O-2, D-2, and N-2 by using a laser-vaporization source, low-pressure reaction cell and photoionization time-of-flight mass spectrometer. The reaction probability in a collision between a cluster and a gas molecule was determined for each gas for the first and second molecule. The reactivity was measured at two different cluster-source temperatures: room temperature (RT) and liquid-nitrogen temperature (LNT). We find that vanadium clusters react readily with all molecules investigated. With CO, NO, and O2, the reaction probability is high and exhibits relatively weak size dependence. With D-2 and N-2, the overall reaction probability is lower, and significant size variations are observed over the whole size range investigated, with coinciding minima and maxima for the two molecules. Upon cooling of the cluster source to LNT, the reactivity increases, but the overall size dependence is very similar to that observed at RT. The reaction probability with the second molecule, S-2, is lower than that with the first one, S-1, for all gases investigated, and, in most cases, the size dependence in S-1 and S-2 is similar. By analyzing the total relative abundance of each cluster size as a function of reaction-cell pressure, we find that reaction of V-n with CO, NO, and O-2 results in size-dependent cluster-product fragmentation of clusters in the size range n approximate to 10-20, most likely by metal-atom loss. (C) 1999 American Institute of Physics. [S0021-9606(99)70705-1].