Prompt and delayed dissociation dynamics of dicationic HCN induced by electron impact.

We investigate the dissociation pathways of doubly ionized hydrogen cyanide (HCN2+) produced via 1.0 keV electron beam impact. Using a coincidence ion imaging spectrometer, we identify two distinct dissociation mechanisms: prompt decomposition, characterized by localized correlation islands in time-of-flight spectra, and delayed fragmentation, evidenced by elongated spectral tails. Kinetic energy release distributions indicate that the deprotonation channel (HCN2+ → H+ + CN+) stems from low-lying electronic states of the dication, aligning with prior photon double-ionization studies. However, metastable state lifetimes exhibit significant prolongation compared to photon-induced processes. Calculations of potential energy surfaces combined with reaction rate theory suggest that this discrepancy may arise from differences in vibrational state populations between the two ionization methods.