High-energy collision induced dissociation of iridium hexa-halide dianions: Observation of triple electron detachment and other decay pathways

Lifetimes of the IrBr62− and IrCl62− gas-phase ions were measured in an electrostatic ion storage ring as 3.3 ± 0.1 s and 3.1 ± 0.1 s, respectively. The lifetimes indicate that the dianions are not subject to spontaneous decay under ambient conditions, since they are associated with decay resulting solely from high-energy collisions with residual gas (∼5 × 10−11 Torr) that is present in the ring. To further investigate the high-energy collisional decay dynamics, IrBr62− and IrCl62− were subjected to high-energy collision induced dissociation measurements in an accelerator mass spectrometer (ion translational energy in laboratory frame = 100 keV). A number of daughter ions were formed following the high-energy collisions (e.g., IrCl62− produced IrCl6−, IrCl5−, IrCl4−, IrCl3− and Cl−). The presence of the intact monoanion (i.e., IrCl6−) indicates that electron detachment is a prominent decay process, in contrast to low-energy collisional excitation where IrCl5− and Cl− are produced via ionic fragmentation. The predominance of electron detachment occurring as a result of high-energy collisions was further illustrated by charge-reversal measurements where cationic daughter fragments were observed, consistent with triple electron detachment. This measurement indicates that high-energy collisional activation of dianions should represent a general approach for studying triple electron detachment of molecular anions.