Photoelectron spectra of small LaOn- clusters:: decreasing electron affinity upon increasing the number of oxygen atoms

We present mass selected photoelectron spectra of small lanthanum oxide cluster anions LaOn- (n = 1 - 5) which have been generated in a laser vaporization cluster source. The electron affinity of the lanthanum oxide clusters drops continuously with the number of chemisorbed oxygen atoms as revealed from the anion photoelectron spectra. The decreasing electron affinity behaves contrary to several other metal oxide clusters. The geometry of some of the measured clusters are discussed in comparsion with configuration interaction and density functional calculations using a Gaussian94 program package.