Hydrocarbon-Bond Rearrangements in
Intense Few-Cycle Laser Fields
Matthias Kübel-Schwarz
Fakultät für Physik, Ludwig-Maximilians-Universität München
Email: matthias.kuebel@mpq.mpg.de
Chemical reactions involving the rearrangement of C-H bonds are ubiquitous in nature. The capability to
steer such rearrangements towards a desired outcome is key to controlling complex reactions in organic
molecules. Recently, it has been demonstrated that waveform controlled few-cycle laser pulses can be used
to selectively break C-H bonds in acetylene [1,2].
Here, we go beyond simple dissociation reactions and explore control of the directionality of bond
rearrangement in hydrocarbons (acetylene and allene) by means of phase-controlled few-cycle pulses.
Charged fragments arising from the interaction of each molecule with the intense laser pulse are detected
in coincidence using a reaction microscope. The experimental results are interpreted in terms of a quantum
mechanical model [1,3] where the carrier-envelope phase (CEP) of the driving laser pulse manipulates the
phases of a vibrational wavepacket.
In a second step, we monitor the
temporal evolution of hydrogen
migration by coulomb explosion imaging
with a time-delayed probe pulse,
reconstructing the transient molecular
structure from the detected ion
momenta.
The
isomerization
of
acetylene to vinylidene is tracked by
breakage of both C-H bonds in the
Fig. 1 Molecular Newton plots visualizing the isomerization of acetylene to
trication and coincident detection of all vinylidene. The transient molecular structures are imaged by detecting all ions
three fragments. This allows for arising from the Coulomb explosion channel C2H23+  H++H++C2+ in
capturing a “movie” of the isomerization coincidence. The momentum distributions for C2+ ions and one proton are
in the frame where the momentum of the other proton (not shown) is
(see Fig. 1) and measuring the H-CC-H displayed
fixed along p||. The atomic symbols and molecular bonds are drawn to guide the
bond angle as a function of time delay. eye towards the part of the signal from molecules undergoing isomerization.
The H-CC-H bond angle corresponds to The snapshots were obtained for different time delays as indicated, and
the reactive coordinates along which the averaged over ±14 fs.
isomerization is calculated. Hence, the results of our pump-probe measurements can directly be compared
to the wavepacket propagation simulations used to model the strong-field control of hydrogen migration in
acetylene.
References
[1] A.S. Alnaser et al., Nat. Communic. 5, 3800 (2014)
[1] S. Miura, et al., Chem. Phys. Lett. 595, 61 (2014).
[3] M. Kübel-Schwarz et al., in preparation.