Stierhof, J.; Kühn, S.; Winter, M.; Micke, P.; Steinbrügge, R.; Shah, C.; Hell, N.; Bissinger, M.; Hirsch, M.; Ballhausen, R.; Lang, M.; Gräfe, C.; Wipf, S.; Cumbee, R.; Betancourt-Martinez, G.L.; Park, S.; Niskanen, J.; Chung, M.; Porter, F.S.; Stöhlker, T.; Pfeifer, T.; Brown, G.V.; Bernitt, S.; Hansmann, P.; Wilms, J.; Crepso López-Urrutia, J.R.; Leutenegger, M.A.: A new benchmark of soft X-ray transition energies of Ne, CO2, and SF6: paving a pathway towards ppm accuracy. The European Physical Journal D 76 (2022), p. 38/1-13
10.1140/epjd/s10053-022-00355-0
Open Access Version
Abstract:
A key requirement for the correct interpretation of high-resolution X-ray spectra is that transition energies are known with high accuracy and precision. We investigate the K-shell features of Ne, CO2, and SF6 gases, by measuring their photo ion-yield spectra at the BESSY II synchrotron facility simultaneously with the 1s–np fluorescence emission of He-like ions produced in the Polar-X EBIT. Accurate ab initio calculations of transitions in these ions provide the basis of the calibration. While the CO2 result agrees well with previous measurements, the SF6 spectrum appears shifted by ∼0.5 eV, about twice the uncertainty of the earlier results. Our result for Ne shows a large departure from earlier results, but may suffer from larger systematic effects than our other measurements. The molecular spectra agree well with our results of time-dependent density functional theory. We find that the statistical uncertainty allows calibrations in the desired range of 1–10 meV, however, systematic contributions still limit the uncertainty to ∼40–100 meV, mainly due to the temporal stability of the monochromator energy scale. Combining our absolute calibration technique with a relative energy calibration technique such as photoelectron energy spectroscopy will be necessary to realize its full potential of achieving uncertainties as low as 1–10 meV.