Abstract
An optical study of dilute gold-nickel alloys is described where the nickel impurity forms a virtual bound state in the gold hose. The measurements extended from 0.1 eV to 4 eV and the alloys were in the range 1 to 5 at.%. The results are analysed in terms of a consistent model of the virtual bound state dielectric constant which includes s, p and d phase shifts of the impurity potential and changes in the conduction electron effective mass induced by alloying. The results are compared with the recent infrared low temperature absorptance measurements. Theories of the virtual bound state and a calculation of the width and position of this impurity state are considered.