X-ray-Induced Fragmentation of Isothiocyanic Acid, HNCS

We studied the X-ray-induced fragmentation of isothiocyanic acid, HNCS, following core ionization and excitation at the N1s, C1s, and S2p edges by Auger electron-ion coincidence spectroscopy. Mostly similar fragmentation products were identified at the different edges for normal and resonant Auger-Meitner decay, respectively. Upon normal Auger-Meitner decay, the dication was found to dissociate predominantly by C-S bond cleavage into HNC⁺ + S⁺ and CN⁺ + S⁺ ion pairs. The higher yield of undissociated HNCS²⁺ after S2p ionization is explained by a propensity for the population of low-binding energy final states at this edge. Following resonant core excitation into the 13a' or 4a″ orbital, S⁺ was found to be the main fragment, followed by HNC⁺. Fragments that require isomerization were observed with low yields after both core ionization and excitation. A comparison to isocyanic acid, HNCO, revealed significant differences in the fragmentation pattern of the two molecules.