Disentangling ultraviolet-induced dissociation pathways of 1,2-dichloroethylene using time-resolved Coulomb explosion imaging

We present a study of the ultraviolet (196 nm)-induced photodissociation dynamics of the cis and trans isomers of 1,2-dichloroethylene (C₂H₂Cl₂) using time-resolved Coulomb explosion imaging with 28-fs near-infrared (790 nm) laser pulses. Delay-dependent ion yields and kinetic energy release distributions are used as key observables to disentangle multiple dissociation mechanisms and elimination channels, including H, H₂, HCl, Cl, and Cl₂, loss, and to extract isomer-specific dissociation dynamics for each of these channels. We also observe neutral three-body dissociation into C₂H₂ + Cl + Cl, with contributions from both, a concerted and a sequential breakup mechanism that are strongly isomer specific. Our data suggests that Cl elimination occurs on both the ground and excited states, while HCl, H, and H­­₂ elimination occurs on the ground state manifold for both the isomers. The molecular Cl­₂ elimination channel shows strong isomer dependence suggesting that it involves only the ground state in the cis isomer, while it involves both the ground and excited states in the trans isomer. Our study provides new insight into isomer-specific photodissociation mechanisms and demonstrates the power of time-resolved Coulomb explosion imaging in disentangling complex reaction pathways.