High-resolution movies of molecular rotational dynamics captured with ultrafast electron diffraction

Abstract

Imaging the structure of molecules during a photoinduced reaction is essential for elucidating reaction mechanisms. This requires high spatiotemporal resolution to capture nuclear motions on the femtosecond and subangstrom scale, and a sufficiently high signal level to sample their continuous evolution with high fidelity. Here we show that, using high-repetition-rate ultrafast electron diffraction, we can accurately reconstruct a movie of the coherent rotational motion of laser-aligned nitrogen molecules. We have used a tabletop 90-keV photoelectron gun to simultaneously achieve high temporal resolution of 240 fs full width at half maximum and an electron beam current that is more than an order of magnitude above the previous state of the art in gas-phase ultrafast electron diffraction. With this, we have made an essentially continuous real-space experimental movie of the rotational motion of the molecular wave packet as it evolves from initial alignment and past multiple revivals.