Identification of absolute geometries of cis and trans molecular isomers by Coulomb Explosion Imaging

An experimental route to identify and separate geometric isomers by means of coincident Coulomb explosionimaging is presented, allowing isomer-resolved photoionizationstudies on isomerically mixed samples. We demonstrate the technique on cis/trans 1,2-dibromoethene (C2H2Br2). The momentum correlation between the bromineions in a three-body fragmentation processinduced by bromine3d inner-shell photoionizationis used to identify the cis and trans structures of the isomers. Lastly, the experimentally determined momentum correlations and the isomer-resolved fragment-ion kinetic energies are matched closely by a classical Coulomb explosionmodel.