High‐Resolution Angle‐Resolved Photoelectron Spectroscopy of Cu5−Cu₅⁻ Clusters

Angle‐resolved photoelectron spectroscopy (ARPES) has been used to probe the electronic and vibrational structure of the cluster. High‐resolution spectra recorded near the detachment threshold reveal well‐resolved vibrational progressions, enabling a precise determination of the adiabatic electron affinity (EA = 1.8947(12) eV). Measured vibrational frequencies are in good agreement with density‐functional‐theory predictions, allowing the assignment of the observed modes. The anisotropy parameter of the photoelectron angular distribution from the highest occupied molecular orbital follows the universal momentum‐dependent behaviour recently predicted. In some cases exhibits a dependence on the final vibrational excitation of the cluster which deviates from the prediction, revealing a possible influence of autoionizing excited states.