The M-Series X-Ray Absorption Spectra of Osmium, Iridium, and Platinum

Using a metal x-ray tube and vacuum spectrometer of the Siegbahn type, the absorption spectra of osmium (76), iridium (77), and platinum (78) have been investigated from 3.5A to 7A. Spectrograms have been obtained showing five discontinuities for osmium at 6.194A ($M_1$), 5.975A ($M_2$), 5.027A ($M_3$), 4.412A ($M_4$), and 4.037A ($M_5$); four for iridium at 5.961A ($M_1$), 5.754A ($M_2$), 4.851A ($M_3$), and 4.270A ($M_4$); four for platinum at 5.736A ($M_1$), 5.541A ($M_2$), 4.674A ($M_3$), and 3.738A ($M_5$). Discontinuities corresponding to an $M_5$ level for iridium and an $M_4$ level for platinum were not obtained. The results are shown to be consistent with those of other investigators for tungsten and bismuth. Comparison between experimental values of ${\left(\frac{\nu }{R}\right)}^{\frac{1}{2}}$ and those computed by Bohr and Coster and Sommerfeld reveals some disagreement, the probable cause for which is discussed. Two types of absorption discontinuities were found on the spectrograms—"limits" separating regions of unequal darkening and "white line" absorption. Although, for each element, the same absorbing screen was used throughout, the first two discontinuities, corresponding to $M_1$ and $M_2$, for each element appeared as "limits" while the discontinuities $M_3$, $M_4$, and $M_5$ appeared as "white lines." Photometric curves are shown in support of this conclusion. Attention is called to the bearing of the phenomenon on the theory of "white lines." No evidence was found of a component on the short wave-length side of $M_3$ as was reported by Zumstein for tungsten.