The Arc Spectrum of Osmium

Over 1050 osmium lines have been classified as transitions between 137 terms of Os I. $J$ values have been assigned to all terms without the aid of Zeeman effect studies. If Hund theory is to apply to Os I then the $J$ assignment is unique. The classification is consistent as regards absorption lines, persistent lines, intensities, and comparison with analogous spectra. Comparison with iron shows that nearly all the terms from $d^6{s}^2$ and $d^{7}s$ found in Fe I have been found in Os I. The normal state of osmium is $5d^{6}6s^2\left({}_{}{}^5{}_{}{}^{}D_4^{}{}_{}{}^{}\right)$. The order of $J=2\mathrm{}$ and $J=3\mathrm{}$ is inverted in the four lowest "multiplets." Electron configurations and "multiplets" overlap to such an extent that the unambiguous assignments of $L$ and $S$ values and electron configurations are impossible for most terms. If the term assumed to be $5d^{6}6s\left({}_{}{}^6{}_{}{}^{}D\right)7s{}_{}{}^7{}_{}{}^{}D_4^{}{}_{}{}^{}$ is correctly designated, then a simple series calculation gives 8.7 volts as an approximate value for the ionizing potential of osmium. New wave-length measurements to extend the analysis are to be made using a grating having a dispersion of 0.4A/mm in the second order. Evidence is presented to show that the normal electron configuration of iridium is $5d^{7}6s^2$.