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

Photoelectron angular distributions for the 2PIsub(3/2, 1/2)(pπ)-1 and 2Σ+sub(1/2)(psigma)-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 2PIsub(3/2) and 2PIsub(1/2) 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+(psigma)-1 ionic states are significantly smaller than for the 2PI(pπ)-1 states, in contrast to recent predictions based on angular momentum transfer theory. (orig.)