Electron and fluorescence spectra of a water molecule irradiated by an x-ray free-electron laser pulse

Julia M. Schäfer, Ludger Inhester, Sang-Kil Son, Reinhold F. Fink, and Robin Santra

[BibTeX][pdf]doi:10.1103/PhysRevA.97.053415

With the highly intense x-ray light generated by x-ray free-electron lasers (XFELs), molecular samples can be ionized many times in a single pulse. Here we report on a computational study of molecular spectroscopy at the high x-ray intensity provided by XFELs. Calculated photoelectron, Auger electron, and x-ray fluorescence spectra are presented for a single water molecule that reaches many electronic hole configurations through repeated ionization steps. The rich details shown in the spectra depend on the x-ray pulse parameters in a nonintuitive way. We discuss how the observed trends can be explained by the competition of microscopic electronic transition processes. A detailed comparison between spectra calculated within the independent-atom model and within the molecular-orbital framework highlights the chemical sensitivity of the spectral lines of multiple-hole configurations. Our results demonstrate how x-ray multiphoton ionization-related effects such as charge-rearrangement-enhanced x-ray ionization of molecules and frustrated absorption manifest themselves in the electron and fluorescence spectra.

Tags: XMOLECULE, Auger, fluorescence, photoionization, H2O, CREXIM, frustrated absorption, XFEL, CFEL, DESY