Dynamics of the Photofragmentation of Ketene 3-Cyclopentenone, 3,5-Cycloheptadienone, and Tropone

摘要

Photofragment infrared fluorescence methods were used to study energy disposal to the carbon monoxide product of ketone photodissociation. Vibrationally excited CO is formed upon photolysis at 193 nm, but not at 249 and 308 nm. The nascent CO vibrational energy distribution can be characterized by a temperature, T subscript V = 3750 K. The nascent CO rotational energy distribution can be characterized by a temperature, T subscript r = 6700 K. This suggests that ketone undergoes dissociation by a non-linear path following photoexcitation at 193 nm. Time-resolved laser absorption spectroscopy was used to study the energy partitioning in the photoactivated fragmentation of 3-cyclopentenone, 3,5-cycloheptadienone, and tropone. The CO product vibrational energy distribution was measured at photolysis wavelengths of 193, 249, and 308 nm. The experimental distributions are analyzed by comparing them with distributions calculated by using a statistical model. For 3-cyclopentenone and tropone, only the non-fixed energy of the transition state is available for partitioning among the products' vibrational degrees of freedom, whereas, for 3,5-cycloheptadienone, the full reaction exoergicity is available to be randomly distributed among all the developing products' degrees of freedom. This suggests that the products of the dissociation of 3-cyclopentenone and tropone are vibrationally decoupled from one another in the exit channel. (Author)