The σ⁻/σ⁺ asymmetry in the scattering of excited Na(3²P₃/₂) and K(4²P₃/₂) atoms with oriented electronic angular momentum from rare gas targets has been systematically studied. The orientation is achieved by exciting the atoms with circularly polarized laser light, which is directed perpendicularly into the scattering plane. The origin of the asymmetry is discussed on the basis of the close coupling formalism. This reveals the centrifugal part of the interaction to be the only central reason. The asymmetry is obsd. for all of the different target gases studied (Ne, Ar, Kr, Xe). Quant. the obsd. features change strongly for the different combinations. Model calcns. are presented which show the different fine-structure splitting of the alkali atom and the polarizability of the rare gas atoms to be responsible for the variation.