| Determining the structure of molecules during a chemical reaction is a long-standing goal of physical chemists. Recent developments in laser technology, enables pump-probe experiments to monitor chemical dynamics on a femtosecond time scale. Spectroscopy gives information about the energy levels accessed during a reaction, from which structural parameters are deduced. Electron diffraction gives a direct measure of molecular structures, and when used in the pump-probe scheme, it can give information about transient structures.; We have employed this experiment to study the photo induced ring-opening reaction of 1,3-Cyclohexadiene (CHD). Upon excitation by a UV photon, CHD forms a close hexatriene (HT) structure. In the condensed phase, the HT is observed to quickly isomerize to a longer open chain. The initial opening step is extremely fast, but the isomerization is thought to take several picoseconds. It is the isomerization process that we hope to observe using time resolved electron diffraction.; Our diffraction results do show the product structures of the CHD ring-opening reaction. No isomerization was observed between 3 and 43 ps. The results show an intensity increase in the diffraction signal over a 20 ps period, which is thought to be the electron pulse duration. Problems in identifying the products stems for approximations made in the theory, and the use of ground state structures to serve as theoretical models. |
