Decay of and OCS after sulphur 1s photoexcitation: I. Total ionic charge spectra and electronic processes

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Abstract
Deep core excitation of a small molecule leads to ejection of several electrons and dissociation into numerous alternative sets of fragment ions. We describe an experiment which identifies complete such sets arising from decay of triatomic molecules (and measures their total charge) via triply coincident detection in a time-of-flight mass spectrometer. Careful data correction furthermore enables estimation of contributions from channels comprising one neutral fragment. and OCS molecules were photoexcited by monochromatic x-rays tuned through the entire region around the sulphur 1s threshold (2478 eV). For the first time energy dependent total photoion charge spectra were obtained for deep core excited molecules. They closely resemble those of argon at its K edge, demonstrating the similarity of electronic de-excitation. Electronic processes reflected in these spectra are ejection of excited valence or Rydberg electrons via shake-off and/or Auger decay, photoelectron recapture by post-collision interaction with a fast Auger electron, and pre-edge 1s ionization which extends to tens of eV below threshold. Results on the dissociative aspects are given in the following paper.