Neutral Sulfur Formation in SF₆ Under X-Ray Exposure

In 1978, Joseph Nordgren and Hans Ågren at Uppsala University discovered a spectral anomaly in sulfur hexafluoride (SF₆), which remained a mystery for over four decades. In a collaboration with scientists in Paris, Berlin, and Jena they have revisited the problem. The experiments used 2.5 keV X-rays at the synchrotron facility PETRA III in Hamburg to create deep inner vacancies in sulfur, while recording soft X-rays, emitted subsequent to molecular dissociation into fragments. Advanced theoretical calculations employed to interpret the soft X-ray emission ruled out molecular fragments (e.g., sulfur bound to fluorine atoms) or any charged atomic sulfur states.

It was determined that, despite the ejection of multiple electrons during the decay cascade, neutral sulfur atoms were subsequently forming and emitting soft X-rays. This finding is surprising and unexpected given the strong electron-attracting nature of fluorine atoms. The research highlights the intricate electron density redistribution during the decay process and underscores the power of modern X-ray techniques in solving long-standing scientific puzzles.

This research not only resolves a decades-old mystery but also advances our understanding of molecular dynamics under X-ray exposure. The findings have significant implications for both scientific research and practical applications. It provides crucial insights into the complex molecular response to deep inner-shell ionization, and demonstrates the enduring value of persistence and innovation in scientific discovery.