Photoelectron imaging and theoretical investigation of bimetallic Bi1-2Ga0-2- and Pb-1-4(-) cluster anions

摘要

We present the results of photoelectron velocity-map imaging experiments for the photodetachment of small negatively charged BimGan (m=1-2, n=0-2), and Pb-n (n=1-4) clusters at 527 nm. The photoelectron images reveal new features along with their angular distributions in the photoelectron spectra of these clusters. We report the vertical detachment energies of the observed multiple electronic bands and their respective anisotropy parameters for the BimGan and Pb-n clusters derived from the photoelectron images. Experiments on the BiGan clusters reveal that the electron affinity increases with the number of Ga atoms from n=0 to 2. The BiGa2- cluster is found to be stable, both because of its even electron number and the high electron affinity of BiGa2. The measured photoelectron angular distributions of the BimGan and Pb-n clusters are dependent on both the orbital symmetry and electron kinetic energies. Density-functional theory calculations employing the generalized gradient approximation for the exchange-correlation potential were performed on these clusters to determine their atomic and electronic structures. From the theoretical calculations, we find that the BiGa2-, Bi2Ga3- and Bi2Ga5- (anionic), and BiGa3, BiGa5, Bi2Ga4 and Bi2Ga6 (neutral) clusters are unusually stable. The stability of the anionic and neutral Bi2Gan clusters is attributed to an even-odd effect, with clusters having an even number of electrons presenting a larger gain in energy through the addition of a Ga atom to the preceding size compared to odd electron systems. The stability of the neutral BiGa3 cluster is rationalized as being similar to BiAl3, an all-metal aromatic cluster.