Tracing ultrafast hydrogen migration in allene in intense laser fields by triple-ion coincidence momentum imaging.

Ultrafast hydrogen migration in allene (CH(2)=C=CH(2)) in intense laser fields was investigated by triple-ion coincidence momentum imaging. The migrating proton covering the entire range of an allene molecule was visualized by the momentum correlation maps and by the geometrical structure of triply charged allene reconstructed from the observed momentum vectors of fragment ions. The extent of hydrogen migration was found to play a decisive role in breaking selectively one of the two initially equivalent C-C chemical bonds that become inequivalent in the course of the hydrogen migration.