  The fragmentation dynamics of 2,6- and 3,5-difluoroiodobenzene after iodine
4$d$ inner-shell photoionization with soft X-rays are studied using coincident
electron and ion momentum imaging. By analyzing the momentum correlation
between iodine and fluorine cations in three-fold ion coincidence events, we
can distinguish the two isomers experimentally. Classical Coulomb explosion
simulations are in overall agreement with the experimentally determined
fragment ion kinetic energies and momentum correlations and point toward
different fragmentation mechanisms and time scales. While most three-body
fragmentation channels show clear evidence for sequential fragmentation on a
time scale larger than the rotational period of the fragments, the breakup into
iodine and fluorine cations and a third charged co-fragment appears to occur
within a few hundred femtoseconds -- a time scale larger than the rotational
period of the fragments, the breakup in other channels appears to occur within
a few hundred femtoseconds.
