  Following the changes in molecular structure throughout the entirety of a
chemical reaction with atomic resolution is a long-term goal in femtochemistry.
Although the development of a plethora of ultrafast technique has enabled
detailed investigations of the electronic and nuclear dynamics on femtosecond
time scales, direct and unambiguous imaging of the nuclear motion during a
reaction is still a major challenge. Here, we apply time-resolved Coulomb
explosion imaging with femtosecond near-infrared pulses to visualize the
ultraviolet-induced ultrafast molecular dynamics of gas-phase furan. Widely
contradicting predictions and observations for this molecule have been reported
in the literature. By combining the experimental Coulomb explosion imaging data
with ab initio molecular dynamics and Coulomb explosion simulations, we reveal
the presence of a strong ultrafast ring-opening pathway upon excitation at 198
nm that occurs within 100 fs.
