Ultrafast Dynamics of Isolated Phenylcarbenes Followed by Femtosecond Time-Resolved Velocity Map Imaging

The ultrafast dynamics of two carbene model systems, chlorophenylcarbene (CPC) and trifluoromethylphenylcarbene (TFPC), has been studied in a molecular beam. Velocity map imaging aids optimizing the pyrolysis conditions for a clean generation of reactive intermediates by supersonic jet flash pyrolysis. The dynamics was followed in real time by time-resolved mass spectroscopy and photoion and photoelectron imaging. CPC was excited at 265 nm into the 3 1A′ state, corresponding to excitation from a π-orbital of the aromatic ring into the lowest unoccupied molecular orbital, which contains the p-orbital at the carbene center. The experimental results suggest a three step deactivation process in agreement with computations. TFPC exhibits two absorption bands in the 36000 cm−1 and 41000 cm−1 range and gives rise to very similar dynamics, although it has a triplet ground state. The experimental data were augmented by computations.