The first direct experimental observation of an intramolecular reaction path going through a transition state is reported. The results of a Coulomb explosion imaging experiment for cold ${\mathrm{CH}}_4^{+}$ molecular ions show the intermediate conformations between permutationally equivalent structures of this molecule. Comparison with a theoretical prediction of the corresponding reaction path is given and the agreement is satisfactory.

• Received 26 February 1993

DOI:https://doi.org/10.1103/PhysRevLett.70.3549