Isomerization of a highly excited vibrational state of acetylene was studied using the Coulomb explosion imaging technique. A vinylidene isomer was prepared by electron photodetachment of the negative molecular ion and the corresponding distribution function of the nuclear configurations of the molecule was sampled after a time period of $3.5\mu \mathrm{s}$. The population of the vinylidene isomer was found to be significantly high ( $\sim 50\%$), in contrast to the commonly accepted notion of vinylidene as a short-lived isomer.

• Received 20 January 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.3347