The Differences Between theM5andM4Absorption Edges of Gold in the Pure Metal and in a Gold-Copper Alloy

Abstract

The suggestion that the discrepancies between observed and computed energies of the $M_4$ and $M_5$ absorption edges arise because transitions occur from the $M_4$ and $M_5$ levels to lattice levels, the transitions being governed by some selection rule, was investigated. The $M_4$ and $M_5$ edges of gold in the pure state and in a 50 atomic percent copper-gold alloy were photographed in a vacuum spectrometer. The change of lattice constant from 4.06A for gold to 3.86A for the alloy, which caused the energies of the lattice levels to change, produced shifts toward higher energies in Au $M_5$ of 2.5 electron volts and in Au $M_4$ of 6.8 electron volts. This shows that the final levels of these edge transitions are lattice levels. The results give credence to the assumption that, upon assigning to the low lattice levels the values of $l$ which they have in free atoms, there are preferred atomic to low lattice level transitions which are often given by $\Delta l=\pm 1$. Data of other investigators are cited to support the view that the final levels in absorption are lattice levels and that the $l$ selection rule is in evidence.