Isotope effect in the electron-impact-induced delayed dissociation of benzene dications

When molecules lose two electrons upon collisions with electrons, photons, or high-energy ions, the resulting molecular ions undergo direct dissociation or delayed dissociation under the influence of intramolecular Coulomb repulsion. The lifetime of metastable ions in delayed dissociation is crucial for understanding molecular properties and dissociation dynamics. In this study, we performed an experimental investigation on the dissociation dynamics of benzene dications induced by 200 eV electron-impact using a reaction microscope imaging spectrometer. Through ion momentum coincidence measurements, we identified two different dissociation mechanisms for the CH3+ + C5H3+ and CH3+ + 13CC4H3+ channels: direct dissociation and delayed dissociation. By analyzing the time-of-flight difference between the two fragment ions, we derived the lifetimes of the metastable dications C6H62+ and 13CC5H62+, which were determined to be 1160 ± 34 and 370 ± 28 ns, respectively. The results demonstrate that 13C isotopic substitution significantly reduces the lifetime of metastable benzene dications, highlighting the critical role of the isotopic effect in regulating the delayed dissociation dynamics of benzene dications.