Abstract
An experimental route to identify and separate geometric isomers by means of coincident Coulomb explosion imaging is presented, allowing isomer-resolved photoionization studies on isomerically mixed samples. We demonstrate the technique on cis/trans 1,2-dibromoethene (C2H2Br2). The momentum correlation between the bromine ions in a three-body fragmentation process induced by bromine 3d inner-shell photoionization is used to identify the cis and trans structures of the isomers. The experimentally determined momentum correlations and the isomer-resolved fragment-ion kinetic energies are matched closely by a classical Coulomb explosion model.
Highlights
An experimental route to identify and separate geometric isomers by means of coincident Coulomb explosion imaging is presented, allowing isomer-resolved photoionization studies on isomerically mixed samples
We concentrate on the three-body fragmentation channel C2H+2 +Br+ +Br+, for which we measure the time of flight and hit positions of all three fragments in coincidence
The coincidence Coulomb explosion imaging technique is a promising candidate in this respect, and was used already in a number of time-resolved experiments studying, e.g., the isomerization between acetylene and vinylidene[11,12,13,14,15]
Summary
An experimental route to identify and separate geometric isomers by means of coincident Coulomb explosion imaging is presented, allowing isomer-resolved photoionization studies on isomerically mixed samples. A prototypical example is the isomerization between acetylene (HCCH) and vinylidene (H2CC) via hydrogen migration, which has been studied, e.g. using synchrotron radiation[10] and by femtosecond time-resolved experiments with intense, ultrashort optical[11,12] and XUV or X-ray pulses[13,14,15] All of these experiments have employed the Coulomb explosion coincidence momentum imaging technique[16,17,18,19], in which all charged fragments that are created when the multiply charged parent ion breaks up (“explodes”) are measured in coincidence and their momentum vectors are used to extract information about the dynamical change in the geometry of the parent molecule. Our methodology is directly applicable to time-resolved pump-probe experiments studying the cis-trans isomerization using either strong-field or inner-shell ionization as a probe since it allows performing an in-situ measurement of the isomer ratio of an isomerically mixed sample
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