Excited state molecular structures and reactions directly determined by ultrafast electron diffraction
In this communication, we report on the use of ultrafast electron diffraction to determine structural dynamics of excited states and reaction products of isolated aromatic carbonyls, acetophenone and benzaldehyde. For a 266 nm excitation, a bifurcation of pathways is structurally resolved, one leading to the formation of the triplet state (quinoid structure) and another to chemical products: for benzaldehyde the products are benzene and carbon monoxide (hydrogen migration and bond rupture) while those for acetophenone are the benzoyl and methyl radicals (bond rupture). The refined structures are compared with those predicted by theory. These dark structures and their radiationless transitions define the reduced energy landscape for complex reactions.
Additional Information© 2005 American Institute of Physics. (Received 31 August 2005; accepted 1 November 2005; published online 14 December 2005) This work was supported by the National Science Foundation and the Air Force Office of Scientific Research. The authors would also like to thank Professor Robert Huber  for a private communication regarding acetaldehyde channels (CH4+CO; CH3+HCO; and H+CH3CO, depending on excitation energy) and his proposal for UED of acetaldehyde, and Dr. Shoujun Xu for his assistance in the design of the inlet system of the apparatus.
Published - FEEjcp05.pdf