Mainz 2017 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 10: Highly Excited Molecules and Clusters
MO 10.2: Vortrag
Mittwoch, 8. März 2017, 15:00–15:15, N 6
Ultrafast Isomerization in Acetylene Dication: To Be or Not To Be — Zheng Li1,2, •Ludger Inhester1, Chelsea Liekhus-Schmaltz2, Oriol Vendrell3, and Todd Martinez2 — 11CFEL, DESY, Notkestr. 85, D-22607 Hamburg, Germany — 2SLAC National Accelerator Laboratory, CA 94025 Menlo Park, USA — 3Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark
The mechanism for ultrafast isomerization of acetylene [HCCH]2+ to vinylidene [H2CC]2+ dication is nebulous. Theoretical studies show a large potential barrier (>2eV) for isomerization pathways, implying that the corresponding isomerization should take picoseconds or even longer. However a recent experiment at a femtosecond X-ray free electron laser (XFEL) suggests that large amplitude hydrogen migration proceeds on a sub-100 femtosecond time scale[1]. We present a complete theoretical study of dynamics of acetylene dication produced by Auger decay after X-ray photoionization of carbon K-shell. We find that isomerization does not occur on the sub-100 fs timescale and is not required to explain the time-resolved Coulomb imaging experiment. This study resolves the seeming contradiction between experiment and theory concerning the isomerization time scale in acetylene dication. This work calls for careful interpretation of structural information from the widely applied Coulomb momentum imaging method but also points out its strengths in mapping out momentum dispersion dynamics even when structural variation is minor[2].
[1] Ch. Liekhus-Schmaltz et al., Nature Commun. 6, 8199 (2015). [2] Z. Li et al., arXiv:1605.05707, submitted.