Photoelectron imaging of small silicon cluster anions, Si(n) (-) (n=2-7).

Photoelectron imaging experiments were conducted on small silicon cluster anions, Si(n) (-) (n=2-7), acquired at a photon energy of 3.49 eV (355 nm). Electronic transitions arising from the anion ground states are observed, and the evaluated vertical detachment energies agree well with previous measurements and theoretical calculations. The anisotropy beta parameters have also been determined for each unique feature appearing in the photoelectron angular distributions at the employed photon energy. Separate calculations using density functional theory are also undertaken to determine the relative atomic orbital contributions constructing the interrogated highest occupied and low-lying molecular orbitals of a specific cluster. A method to interpret the observed cluster angular distributions, term the beta-wave approach, is then implemented which provides quantitative predictions of the anisotropy beta parameter for partial wave emission from molecular orbitals partitioned by varying contributions of atomic orbital angular momenta. Highlighted in the beta-wave analysis is the ability of discriminating between disparate molecular orbitals from two nearly isoenergetic structural isomers of opposing point group symmetry for the Si(4) (-) and Si(6) (-) cluster ions, respectively.