The photoelectron angular distributions of HBr and HI AT hν = 21.2 eV

Photoelectron angular distributions for the ²Π_{$\text{3}\text{2}$, $\text{1}\text{2}$}(pπ)^?1 and ²Σ_{$\text{1}\text{2}$}⁺(pσ)^?1 ionic states of HBr and HI have been measured at a photon energy of 21.2 eV. The asymmetry parameters for the highly localized pπ orbitals closely follow those of the “lone-pair” orbitals of the related CH₃X molecules and the outer np atomic orbitals of the corresponding united atoms. Furthermore, the asymmetry parameters for the ²Π_{$\text{3}\text{2}$} and ²Π_{$\text{1}\text{2}$} states were found to be equal within experimental uncertainty, despite the large spin—orbit splittings of these heavy molecules. The asymmetry parameters for the ²Σ⁺(pσ)^?1 ionic states are significantly smaller than for the ²Π(pπ)^?1 states, in contrast to recent predictions based on angular momentum transfer theory.