Imaging Coherent Nuclear Motion in Photoexcited Molecules with Ultrafast Electron Diffraction AMOP Seminar

Date: Time: 3:30 pm–4:30 pm
Jorgensen Hall Room: 145
Contact: Physics Department, 472-2770,
Speaker: Kyle Wilkin, Department of Physics & Astronomy, The University of Nebraska-Lincoln

We have used ultrafast electron diffraction (UED) to capture the structural dynamics during the UV photodissociation reaction of 1,2-Diiodotetrafluoroethane (C2F4I2). The experiment was performed at the SLAC UED facility with a 3.7 MeV electron beam where previous experiments have shown femtosecond resolution [1][2][3]. Previously, the Zewail group used UED with 5 ps resolution to study the evolution of photo-dissociated C2F4I2 and found the structure of the transient state C2F4I to be the classical non-bridged structure [4]. No evidence of a bridged structure was found; however, a question remained on whether a bridged structure with a femtosecond lifetime also existed. We have observed that the non-bridged structure forms within 200 fs of the laser excitation, one vibrational period of the C-I bond. After dissociation an oscillation with a 250 fs period is observed in the inter-atomic distances of the transient. Through comparison to numerical simulations, this oscillation has been determined to be a combination of coherent vibrations and rotations in the isolated CF2 group.

[1] J. Yang, M. Guehr, X. Shen, R. Li, T. Vecchione, R. Coffee, J. Corbett, A. Fry, N. Hartmann, and C. Hast et al., “Diffractive Imaging of Coherent Nuclear Motion in Isolated Molecules,” Phys. Rev. Lett. 117, 153002 (2016).
[2] J. Yang, M. Guehr, T. Vecchione, M. S. Robinson, Renkai Li, N. Hartmann, X. Shen, R. Coffee, J. Corbett, A. Fry, K. Gaffney, T. Gorkhover, C. Hast, K. Jobe, I. Makasyuk, A. Reid, J. Robinson, S. Vetter, F. Wang, S. Weathersby, C. Yoneda, M. Centurion & X. Wang, “Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses,” Nature Communications 7, 11232 (2016).
[3] Jie Yang, Xiaolei Zhu, Thomas J. A. Wolf, Zheng Li, J. Pedro F. Nunes, Ryan Coffee, James P. Cryan, Markus Gühr, Kareem Hegazy, Tony F. Heinz, Keith Jobe, Renkai Li, Xiaozhe Shen, Theodore Veccione, Stephen Weathersby, Kyle J. Wilkin, Charles Yoneda, Qiang Zheng, Todd J. Martinez, Martin Centurion, and Xijie Wang, “Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction,” Science 361, 64 (2018).
[4] H. Ihee, B. M. Goodson, R. Srinivasan, V. A. Lobastov, and A. H. Zewail, “Ultrafast Electron Diffraction and Structural Dynamics:? Transient Intermediates in the Elimination Reaction of C2F4I2,” J. Phys. Chem. A 106, 4087-4103 (2002).

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