Ultrafast delocalization of hydrogen atoms in allene in intense laser fields

Ultrafast delocalization of hydrogen atoms in allene (CH₂=C=CH₂) induced by intense laser fields was investigated by the Coulomb explosion coincidence momentum imaging method. On the basis of the kinetic energy distributions of the fragment ions produced through the two three-body Coulomb explosion pathways, C₃H₄³⁺ ? H⁺ + CH⁺ + C₂H₂⁺mathrm{C}_{3}mathrm{H}_{4}^{3+} rightarrow mathrm{H}^{+} + mathrm{CH}^{+} + mathrm{C}_{2}mathrm{H}_{2}^{+} and C₃H₄³⁺ ? H⁺ + C₂H⁺ +CH₂⁺mathrm{C}_{3}mathrm{H}_{4}^{3+} rightarrow mathrm{H}^{+} + mathrm{C}_{2}mathrm{H}^{+} +mathrm{CH}_{2}^{+}, and the proton maps for both pathways, it was shown that the decomposition proceeds in a stepwise manner as well as in a concerted manner. The time scale of the hydrogen migration within an allene molecule was estimated to be ∼20 fs.