IR Multiphoton Dissociation Dynamics of Octafluorocyclopentene: Time-Resolved Observation of Concerted Products :CF2 and Hexafluorobutadiene

Article abstract of DOI:10.1021/j100032a006

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 10⁶s^-1.The fast exponential decay of the transient signal up to 100 μs is assigned to electrocyclic isomerization of HFBD to hexafluorocyclobutene with a rate constant k = (5.7 +/- 0.2) x 10⁴s^-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 10⁷M^-1s^-1.RRKM calculation for the unimolecular dissociation of OFCP and isomerization of HFBD gives an average energy of OFCP as 383 +/- 10kJ/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.