Femtosecond dynamics of hydrogen elimination: benzene formation from cyclohexadiene

Using femtosecond-resolved mass spectrometry in a molecular beam, we report real-time study of the hydrogen elimination reaction of 1,4-cyclohexadiene . The experimental observation of the ultrafast stepwise H-elimination eluc idates the reaction dynamics and mechanism. With density-functional theory (ground-state) calculations, the nature of the reaction (multiple) pathways is examined. With the help of recent conical-intersection calculations, th e excited-state and ground-state pathways are correlated. From these experi mental and theoretical results we provide a unifying picture of the thermoc hemistry, photochemistry and the stereochemistry observed in the condensed phase.