Ultrafast absorption spectroscopy of photodissociated CF₂Br ₂: Details of the reaction mechanism and evidence for anomalously slow intramolecular vibrational redistribution within the CF₂Br intermediate

Ultrafast time-resolved absorption spectroscopy in the hard ultraviolet has been used to investigate the photodissociation of gas-phase CF ₂Br₂ photolyzed at 248 nm. The broadband spectra obtained in the 250-265 nm region have shown that absorption of a single photon activates a two-step sequential elimination of the molecule's two bromine atoms, leaving the product CF₂ radical in the ground or first-excited vibrational state of its ν₂ bending mode. The spectra also demonstrate the direct detection of the vibrationally hot CF₂Br intermediate species itself. We interpret the ∼6 ps time scale over which the diffuse CF ₂Br spectrum evolves as evidence for slow intramolecular vibrational redistribution within this molecule.