Real time observation of:CF2 and hexafluorobutadiene (HFBD) generated simultaneously in the concerted IR multiphoton dissociation of octafluorocyclopentene (OFCP) is reported. The formation rate of both the. transients, i.e., hot HFBD and :CF2, which have an overlapping absorption at 250 nm, fits to a single exponential, with a rate constant (2.0 +/- 0.1) x 10(6) s(-1). The fast exponential decay of the transient signal up to 100 mu s is assigned to electrocyclic isomerization of HFBD to hexafluorocyclobutene with a rate constant k = (5.7 +/- 0.2) x 10(4) s(-1), whereas the slower decay on the millisecond time scale suggests:CF2 dimerization to form C2F4, with a bimolecular rate constant (4.5 +/- 0.1) x 10(7) M(-1) s(-1). RRKM calculation for the unimolecular dissociation of OFCP and isomerization of HFBD gives an average energy of OFCP as 383 +/- 10 kJ/mol and of nascent HFBD as 202 +/- 5 kJ/mol, corresponding to the experimental rates, The nascent vibrationally hot HFBD exhibits a red shift of 50 nm in the transient absorption spectrum.