Physical properties of amorphous solid interstellar material from X-ray absorption spectroscopy of Scorpius X-1

High-quality, high-resolution X-ray spectra were obtained of Sco X-1 with the Reflection Grating Spectrometer (RGS) onboard the XMM-Newton satellite. The spectrum around the oxygen K-edge is searched for signatures indicative for EXAFS. Analysis shows a clear indication of EXAFS with photo-electron scattering distances in the absorbing medium in a range that applies to many solids. When scattering of the photo-electron on Oxygen atoms is assumed, the oxygen-to-oxygen atom distances found are 2.75 Å. This fits with distances as found in amorphous water ice, although water ice is thought to be an unlikely constituent of the diffuse interstellar clouds that form the absorbing medium towards Sco X-1.