Visualizing Recurrently Migrating Hydrogen in Acetylene Dication by Intense Ultrashort Laser Pulses

We demonstrate the visualization of ultrafast hydrogen migration in deuterated acetylene dication (C₂D₂²⁺) by employing the pump-probe Coulomb explosion imaging with sub-10-fs intense laser pulses (9 fs, 0.13 PW/cm², 800 nm). It is shown, from the temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C₂D₂³⁺→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 (~90 fs) and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.