title: Visualization of bond rearrangements in acetylene using near single-cycle laser pulses.
abstract: The migration of hydrogen atoms resulting in the isomerization of hydrocarbons is an important process which can occur on ultrafast timescales. Here, we visualize the light-induced hydrogen migration of acetylene to vinylidene in an ionic state using two synchronized 4 fs intense laser pulses. The first pulse induces hydrogen migration, and the second is used for monitoring transient structural changes via Coulomb explosion imaging. Varying the time delay between the pulses reveals the migration dynamics with a time constant of 54 ± 4 fs as observed in the H++ H++ CC+channel. Due to the high temporal resolution, vibrational wave-packet motions along the CC- and CH-bonds are observed. Even though a maximum in isomerization yield for kinetic energy releases above 16 eV is measured, we find no indication for a backwards isomerization - in contrast to previous measurements. Here, we propose an alternative explanation for the maximum in isomerization yield, namely the surpassing of the transition state to the vinylidene configuration within the excited dication state.
authors.affiliation: Department of Physics, LMU Munich, D-85748 Garching, Germany. christian.burger@mpq.mpg.de and Max Planck Institute of Quantum Optics, D-85748 Garching, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Burger
authors.affiliation: Department of Physics, LMU Munich, D-85748 Garching, Germany. christian.burger@mpq.mpg.de.
authors.forename: Nora G
authors.initials: NG
authors.lastname: Kling
authors.affiliation: Department of Chemistry and Biochemistry, LMU Munich, D-81377 Munich, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Siemering
authors.affiliation: Max Planck Institute of Quantum Optics, D-85748 Garching, Germany and Physics Department, American University of Sharjah, POB2666, Sharjah, UAE.
authors.forename: Ali S
authors.initials: AS
authors.lastname: Alnaser
authors.affiliation: Max Planck Institute of Quantum Optics, D-85748 Garching, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Bergues
authors.affiliation: Department of Physics and Astronomy, King-Saud University, Riyadh 11451, Saudi Arabia.
authors.forename: Abdallah M
authors.initials: AM
authors.lastname: Azzeer
authors.affiliation: Max Planck Institute of Nuclear Physics, D-69117 Heidelberg, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Moshammer
authors.affiliation: Department of Chemistry and Biochemistry, LMU Munich, D-81377 Munich, Germany.
authors.forename: Regina
authors.initials: R
authors.lastname: de Vivie-Riedle
authors.affiliation: Department of Physics, LMU Munich, D-85748 Garching, Germany. christian.burger@mpq.mpg.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kübel
authors.affiliation: Department of Physics, LMU Munich, D-85748 Garching, Germany. christian.burger@mpq.mpg.de and Max Planck Institute of Quantum Optics, D-85748 Garching, Germany.
authors.forename: Matthias F
authors.initials: MF
authors.lastname: Kling