  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.
