Isotopic effects in two-body fragmentation process of water dications induced by electron-impact ionization

Abstract The two-body fragmentation dynamics of water isotopologues dications (H 2 O 2+ , HOD 2+ , and D 2 O 2+ ) induced by 200 eV electron-impact is investigated. Two fragment ions and an emitted electron are detected in coincidence, and their momentum vectors are determined by employing a reaction microscope. The complete kinematical information of four two-body fragmentation channels of H + + OH + , H + + OD + , D + + OH + , and D + + OD + is obtained. By analyzing the projectile energy-loss spectrum, the initial electronic state of the two-body dissociation channel is determined. Upon examining the kinetic energy release (KER) distributions of four fragmentation channels, a clear difference is found between the two-body fragmentation channels H + + OD + and the other three channels. The isotopic effect in the two-body fragmentation is demonstrated by the analysis of the relative yields of the two-body fragmentation channels originating from different isotopologues, which show preferential cleavage of the O-H bond over the O-D bond. These results provide deeper insight into the microscopic dynamic mechanisms in water radiolysis.