On the Fine Structure Splitting of the 3p43d4D5/2 and 3p43d4D7/2 Levels of FE X

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Friday, July 21, 2017

We study UV spectra obtained with the SO82-B slit spectrograph on board SKYLAB to estimate the fine structure splitting of the Cl-like 3p43d4D5/2 and 3p43d4D7/2 levels of Fe X.

Raw S082B image
Raw S082B image with wavelength scale calibrated as described in the text. The image shown is an off-limb exposure, catalog number 3B158 007, a 19 minute 59 second exposure obtained on January 9th 1974 beginning at 18:41 UT. The “intensity” scale shown on the right is photographic density. The images of the spectrograph slit are seen along the abscissa. But because the slit was not in a solar image plane, there is no solar information in the slit direction.

The splitting is of interest because the Zeeman effect mixes these levels, producing a “magnetically induced transition” (MIT) from 3p43d4D7/2 to 3p5 2Po3/2 for modest magnetic field strengths characteristic of the active solar corona. We estimate the splitting using the Ritz combination formula applied to two lines in the UV region of the spectrum close to 1603.2 Å, which decay from the level 3p4(1D)3d2G7/2 to these two lower levels. The MIT and accompanying spin-forbidden transition lie near 257 Å. By careful inspection of a deep exposure obtained with the S082B instrument we derive a splitting of 8.3 ± 0.9 and 3.6 ± 2.7 cm−1.

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