Isomer-selective dissociation dynamics of 1,2-dibromoethene ionised by femtosecond-laser radiation

We study the isomer-specific photoionisation and photofragmentation of 1,2-dibromoethene (DBE) under strong-field fs-laser irradiation in the gas phase complementing previous studies utilising ns- and ps-laser excitation. Our findings are compatible with a dissociative multiphoton-ionisation mechanism producing a variety of ionic photofragments. Using both Stark deflection and chemical separation of the two isomers, pronounced isomer-specific photofragmentation dynamics could be observed for different product channels. While for Br⁺ formation, the isomer specificity appears to originate from different photoexcitation efficiencies, for the C₂H₂Br⁺ channel it is more likely caused by differences in the coupling to the exit channel. By contrast, the formation of the C₂H₂⁺ photofragment does not seem to exhibit a pronounced isomeric dependence under the present conditions. The present work underlines the importance of isomeric effects in photochemistry even in small polyatomics like the present system as well as their pronounced dependence on the photoexcitation conditions.