Diffractive imaging of a molecular rotational wavepacket with femtosecond Megaelectronvolt electron pulses

TL;DR

This study demonstrates femtosecond, sub-Angstrom resolution electron diffraction imaging of molecular rotational wavepackets, capturing real-time nuclear dynamics in nitrogen molecules with unprecedented precision.

Contribution

First use of MeV electron pulses to image molecular rotational dynamics with 100 fs temporal and sub-Angstrom spatial resolution.

Findings

Resolved nuclear positions within molecules during rotation.

Observed transition from aligned to anti-aligned molecular states in 300 fs.

Achieved unprecedented temporal and spatial resolution in molecular imaging.

Abstract

Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, since the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. We performed a gas-phase electron diffraction experiment using Megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved an unprecedented combination of 100 fs root-mean-squared (RMS) temporal resolution and sub-Angstrom (0.76 {\AA}) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions.