Predicting the Photoelectron Spectra of Quasi Octahedral Al₆Mo^- Cluster

We have recently developed a computational methodology to separate the effects of size, composition, symmetry and fluxionality in explaining the experimental photoelectron spectra of mixed-metal clusters. This methodology was successfully applied first in explaining the observed differences between the spectra of Al₁₃^- and Al₁₂Ni^- and more recently to explain the measured spectra of Al_nMo^-, n=3-5,7 clusters. The combination of our approach and new synthesis techniques can be used to prepare cluster-based materials with tunable properties. In this work we use the methodology to predict the spectrum of Al₆Mo^-. This system was chosen because its neutral counterpart is a perfect octahedron and it is distorted to a D_3d symmetry and was not observed in the recent experiments. This high symmetry cluster bridges the less symmetric Al₅Mo^- and Al₇Mo^-structures.The measured spectra of Al₅Mo^- has well defined peaks, while that of Al₇Mo^-does not. This can be explained by the fluxionality of Al₇Mo^-, as at least 6 different structures lie within the range that can be reached by thermal effects. We predict that Al₆Mo^- has well defined peaks, but some broadening is expected as there are two low-lying isomers, one of D_3d and the second of D_3h symmetry that are only 0.052 eV apart.