The spectrum of Au I and Au II has been examined for hyperfine structure in the region $\lambda 2300-6300\mathrm{A}$. Splitting has been observed in more than eight lines of the spectrum of Au I, whereas the hyperfine structure of Au II lines could not be resolved. From the four-component structure of the lines $\lambda 4437\mathrm{A}$ and $\lambda 4607\mathrm{A}$ it is shown that the mechanical moment of the gold nucleus is (3/2) ($\frac{h}{2\pi }$). The effect of self-reversal in the resonance lines has been investigated and eliminated. The magnetic moment determined from the splitting of the unreversed resonance line $\lambda 2428\mathrm{A}$ is found to be 0.195 proton-magneton. No other determination of the magnetic moment is at present possible because of the intermediate coupling shown to exist in the complex electronic configurations of Au I and the inadequacies of the present theory of hyperfine structure. The splitting of the ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ level is estimated and found to be in approximate agreement with that calculated from the ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ level. No indication of any abnormally large ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ separation or of any isotope shift has been found.

• Received 4 August 1938

DOI:https://doi.org/10.1103/PhysRev.55.170