High-Precision Determination of Oxygen-K$\hat{I}\pm$ Transition Energy Excludes Incongruent Motion of Interstellar Oxygen

Abstract

We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O${}_2$ with 8 meV uncertainty. We reveal a systematic $\sim$450 meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O${}_2$ literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.

Accepted by PRL. Main article: 7 pages, 3 figures. Supplemental Material: 3 pages, 5 figures