The Nuclear Spin of Potassium

Photographs of certain bands in the absorption spectrum of the potassium molecule show branches with alternating intensities. Moreover, comparison of the line spacings with those calculated by extrapolating observations on lithium and sodium show that all lines of each branch are present and the phenomenon of alternating missing lines does not occur. This disproves the assertion, based on failure of certain observers to find hyperfine structure, that the nuclear spin of ${\mathrm{K}}^{39}$ is zero.