Strong electric fields that are larger than those of valence electrons in molecules shake out many electrons from the molecules.[1] The generation of highly charged molecular ions by femtosecond laser fields followed by a Coulomb explosion [2] prepares charged atoms in close proximity. The ion dynamics have been investigated by covariance mapping, [3] momentum imaging techniques, [4] and simple consideration of kinetic energy releases. The interaction between ionic species is usually solved by a classical equation of motion under point-charge approximation. Supposing that two charges with different masses exist in close proximity, the light ion flies away while the heavy counterion remains near the original location to conserve momentum. If the heavy ion obstacles disturb the direction in which the precursor ion move, the light ions would undergo structural deformation that enables the light ions to fly away. Linear molecules exposed to intense laser fields would provide interesting information on this issue, especially when the terminal heavy atoms block the movement of lighter ions or ion clusters in the linear molecule. We demonstrate the mass effects on the Coulomb explosion processes of acetylene derivatives of similar geometry but with different electronic orbitals and weights of terminal atoms.We compare the Coulomb explosion dynamics between acetylene and diiodoacetylene (DIA, IÀCCÀI). Multiple ionization was carried out with a 40 fs pulse centered at 800 nm, and the ions were detected by a time-of-flight mass spectrometer. Figure 1 shows the time-of-flight mass spectrum of DIA. The principal ions were C 2 I 2 w + (w = 1À4), C 2
Highlights •Broad ion angular distributions are attributed to imperfect alignment of diiodoalkanes in intense laser fields. •Iodine and carbon ions accompanying large kinetic energies are ejected from longer diiodoalkanes. •Charge localization on the edges of molecules before Coulomb explosion is proposed.
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