Capturing Molecular Motion with Relativistic Electrons

Relativistic Electrons
Image courtesy of SLAC National Accelerator Laboratory Researchers have used relativistic electron pulses to make images of rotating molecules. The molecules are set in rotational motion using a laser pulse. By illuminating the sample with the electron pulses at different times after the laser, the researchers were able to capture very fast changes in the orientation of the molecules. This results demonstrate a temporal resolution sufficient to directly image chemical reactions.

Nitrogen molecules were aligned with a laser pulse, and the subsequent motion of the molecules was imaged with atomic resolution using femtosecond electron pulses.

The Impact

This gas phase electron diffraction experiment, demonstrating 100-femtosecond resolution, breaks a longstanding barrier to resolving molecular geometry changes on the timescale of atomic motion. This new instrument will be used to image the ultrafast evolution of chemical reactions with atomic resolution.

Summary

An important step in understanding chemical reactivity is determining how molecular structure changes during a reaction. The ability to image ultrafast structural changes on their natural time scale has been an elusive goal in the chemical sciences. To address this challenge, researchers at SLAC National Accelerator Laboratory and the University of Nebraska-Lincoln produced and used high-quality femtosecond pulses of electrons accelerated to relativistic energy in a gas-phase electron diffraction experiment. The resulting diffraction images captured the rotational wavepacket dynamics of impulsively laser-aligned nitrogen molecules, demonstrating 100 femtosecond temporal resolution and sub-Angstrom spatial resolution, making it possible to resolve the position of the atoms within the molecule. The diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in just 300 fs. The results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions.