Toward Femtosecond Time-Resolved Inner-Shell Transient Absorption Spectroscopy of Ultrafast Dynamics in Sulfur-Containing Molecules

Sulfur-containing compounds play an important role in many applications such as polythiophene-based organic solar cells or the removal of sulfur compounds by hydrodesulfurization in the petroleum industry. Ultrafast relaxation dynamics (e.g. dissociation, internal conversion and intersystem crossing) of sulfur-containing molecules after photoexcitation have attracted considerable attention as a pathway to a better understanding of the fundamental chemistry of these systems. The novel technique of extreme ultraviolet (XUV) femtosecond transient absorption spectroscopy provides real-time access to the time-dependent structure and transient electronic states of molecules in the vicinity of a specific atom. The usable photon energy range of a high-order harmonic based XUV transient absorption setup has been extended up to 180~eV, enabling measurements in the vicinity of the sulfur 2p edge (165~eV). This new capability opens the route to monitor ultrafast intramolecular dynamics from the unique perspective of well-localized sulfur atoms. Preliminary results will be presented on the photoinduced ultrafast ring-opening, dissociation and vibrational relaxation dynamics in gaseous thiophene (C$_{\mathrm{4}}$H$_{\mathrm{4}}$S) and carbon disulfide (CS$_{\mathrm{2}})$.