Isomerization dynamics of dicationic CS2 and OCS driven by electron-impact

The isomerization of dications of CS2 and OCS is investigated using combined experimental and theoretical methods. The dications were generated by a high-energy electron pulse and the fragment ions were detected by a momentum imaging time-of-flight spectrometer. Bond rearrangement reactions leading to C+ + S2+ and C+ + OS+ were identified through coincident measurements. Theoretically, potential energy surfaces along the reaction paths were calculated using high-level quantum chemistry methods. For CS2+, isomerization is initiated by ionization excitation followed by a decay process. In contrast, the isomerization channel for OCS2+ can open on the ground dicationic state through vibrational excitation. The predicted kinetic energy releases agree with the experimental data. This study demonstrates that, as a common process in dissociative ionization, isomerization mechanism may be influenced by molecular symmetry.