Photoelectron angular distributions in photodetachment from polarised d-like states: the case of HO₂⁻

We present a photoelectron imaging study of the angular distributions in HO₂⁻ photodetachment. The transitions studied correspond to electron detachment from the a ^″ HOMO and a′ HOMO−1 of HO₂⁻, yielding the neutral hydroperoxy radical in the ground and first excited electronic states. The experimental results are analysed using the p-d variant of the general model for photodetachment from mixed-character states. In this model, the parent anion molecular orbitals or the corresponding Dyson orbitals are described as superpositions of atomic p and d functions placed at a chosen centre in the molecular frame. As photoelectron angular distributions are sensitive to the long-range scaling of the parent orbitals, modelling the experimental results yields insight into the asymptotic behaviour of anionic wavefunctions. In the model, the long-range behaviour of diffuse orbitals is parameterised using the effective charges defining the basis functions. These parameters do not correspond to physical charges in the anion, but describe the long-range scaling of the p and d components of the model function and, therefore, the parent anion orbital. The experimental and model results for HO₂⁻ are compared to NO⁻ and O₂⁻, shedding light on the effects of molecular symmetry and chemical bonding structures on the photoelectron angular distributions.