Diffraction methods are used to reconstruct an atomic scale object from the diffraction image. Using ultrashort x-ray or electron pulses allows to view molecules as they undergo geometry changes on a femtosecond time scale. This has far reaching impact for our understanding of light-energy conversion in quantum systems.
In a first experiment, we created a coherent quantum wavepacket on the electronically and vibrationally excited states of the iodine molecule. The resulting wavepcket is shown in the left side picture as a false color plot. After excitation, the wavepacket moves from a short internuclear distance of 2.6 A to about 4 A in only 200 fs. The wavepacket then returns to its original distance at 2.6 A after a full vibrational period of 400 fs.
We use relativistic electron pulses of about 100 fs length with a de Broglie wavelength of 0.3 picometers to image this quantum motion. These electron pulses scatter of the molecular wavepaket and show instantaneous snapshots of the bond length. From a Fourier transformation of the diffraction images, we deduce the internuclear molecular distance of the wavepacket as a function of time (blue circles in the left side picture). The experimental values lie on top of the red dashed line, which displays the center of the wavepacket from image above. . In addition, we have reconstructed a rotational quantum wavepaket in an earlier study .
This research is carried out at the ultrafast relativistic electron source at SLAC National Accelerator Laboratory. We collaborate with the ultrafast electron source group at SLAC as well as the Ultrafast Electron Diffraction (link) group of M. Centurion at Nebraska.
- Diffractive Imaging of Coherent Nuclear Motion in Isolated Molecules
J. Yang, M. Guehr, X. Shen, R. Li, T. Vecchione, R. Coffee, J. Corbett, A. Fry, N. Hartmann, C. Hast, K. Hegazy, K. Jobe, I. Makasyuk, J. Robinson, M. S. Robinson, S. Vetter, S. Weathersby, C. Yoneda, X. Wang, M. Centurion
Phys. Rev. Lett. 115, 173002 (2016)
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- Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses
J. Yang, M. Guehr, T. Vecchione, M. S. Robinson, R. Li, N. Hartmann, X. Shen, R. Coffee, J. Corbett, A. Fry, K. Gaffney, T. Gorkhover, C. Hast, K. Jobe, I. Makasyuk, A. Reid, J. S. Robinson2, S. Vetter, F. Wang, S. Weathersby, C. Yoneda, M. Centurion, X. Wang
Nature Comm. 7, 11232 (2016)
link to article