Mapping the fragmentation of acetylene with femtosecond resolution pump probe at LCLS using multi-particle coincidences

A newly commissioned three-layer delay line anode detector has been used in combination with x-ray pump x-ray probe time-resolved measurement at LCLS. We used $\sim$10 fs long x-ray pulses to probe by coulomb explosion the x-ray initiated ultrafast dynamics in the dication of acetylene (C$_2$H$_2^{+2}$), the smallest hydrocarbon that can isomerize. The dynamics are discerned from the temporal evolution of multi-particle coincidences which we identify by momentum conservation. We compare the results to those of deuterated-acetylene, which should have slower dynamics.