Time-resolved Coulomb explosion imaging of UV-excited diiodomethane

The dynamics in halogenated methanes after UV excitation are of significant interest in the study of light-induced dynamics in gas-phase molecules. Upon UV excitation, diiodomethane (CH₂I₂) can follow multiple pathways resulting in direct C-I bond cleavage and fragment rotation, isomerization, molecular iodine formation, etc.,. We employ time-resolved strong-field Coulomb explosion imaging to directly probe the different pathways. UV light at different wavelengths produced by an optical parametric amplifier (OPA) excites the gas-phase CH₂I₂ molecules, which are probed by a strong ultrafast near-infrared (NIR) pulse. The resulting ions are detected in coincidence using a velocity map imaging spectrometer. Contributions of the different pathways and end products are inferred from the delay-dependent KER spectra, angular distributions, and energy sharing between different ionic fragments.