Visualizing recurrently migrating hydrogen in acetylene dication by intense ultrashort laser pulses.

We demonstrate the visualization of ultrafast hydrogen migration in deuterated acetylene dication (C2D2{2+}) by employing the pump-probe Coulomb explosion imaging with sub-10-fs intense laser pulses (9 fs, 0.13 PW/cm{2}, 800 nm). It is shown, from the temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C2D2{3+}-->D{+} + C{+} + CD{+}, that the migration proceeds in a recurrent manner: the deuterium atom first shifts from one carbon site to the other in a short time scale (approximately 90 fs) and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.