Fragmentation properties of three-membered heterocyclic molecules by partial ion yield spectroscopy: C2H4O and C2H4S

We investigated the photofragmentation properties of two three-membered ring heterocyclic molecules, C2H4O and C2H4S, by total and partial ion yield spectroscopy. Positive and negative ions have been collected as a function of photon energy around the C 1s and O 1s ionization thresholds in C2H4O, and around the S 2p and C 1s thresholds in C2H4S. We underline similarities and differences between these two analogous systems. We present a new assignment of the spectral features around the C K-edge and the sulfur L-2,L-3 edges in C2H4S. In both systems, we observe high fragmentation efficiency leading to positive and negative ions when exciting these molecules at resonances involving core-to-Rydberg transitions. The system, with one electron in an orbital far from the ionic core, relaxes preferentially by spectator Auger decay, and the resulting singly charged ion with two valence holes and one electron in an outer diffuse orbital can remain in excited states more susceptible to dissociation. A state-selective fragmentation pattern is analyzed in C2H4S which leads to direct production of S2+ following the decay of virtual-orbital excitations to final states above the double-ionization threshold.