Site-specific formation of metastable OCS²⁺ studied by Auger-electron-ion coincidence method

We have studied the site-specific formation of metastable OCS²⁺ in the C1s and the O1s Auger decays of OCS molecules by using an Auger-electron-ion coincidence technique. The coincidence measurement reveals the metastable character of the Auger final states with the (3π)^-2 configuration. The formation of metastable OCS²⁺ is observed negligibly in the C1s Auger decay and only weakly in the O1s Auger decay, in contrast to the favorable metastable formation previously reported for S2p Auger decay. It is found that the origin of the site-specificity in the formation of metastable OCS²⁺ arises from the localization effect of the valence orbital involved in the Auger transition. The dissociative dication states related to individual fragmentation pathways are also derived from the coincidence measurement.