Characterization of iso-CF2I2 in frequency and ultrafast time domains

The photolysis of diiododifluoromethane (CF2I2) in condensed phases was studied by a combination of matrix isolation and ultrafast time-resolved spectroscopy, in concert with ab initio calculations. Photolysis at wavelengths of 355 or 266 nm of CF2I2:Ar samples (1:5000) held at similar to 8 K yielded iso-CF2I2 (F2C-I-I), a metastable isomer of CF2I2, characterized here for the first time. The infrared (IR) spectra of this isomer were recorded in matrix experiments, and the derived positions of the C-F stretching modes are in very good agreement with the predictions of high level ab initio calculations, which show that the iso-form is a minimum on the CF2I2 ground state potential energy surface. The formation of this isomer following 350 nm excitation of CF2I2 in room temperature CCl4 solutions was monitored through its intense C-F stretching mode by means of ultrafast time-resolved IR absorption. Together, matrix isolation and ultrafast IR absorption experiments suggest that the formation of iso-CF2I2 occurs via recombination of CF2I radical and I atom. Ultrafast IR experiments detect a delayed rise of iso-CF2I-I absorption, placing an upper limit of 400 fs for the C-I bond dissociation and primary geminate recombination processes. The product absorption spectrum recorded 1 ns after 350 nm excitation of CF2I2 in solution is virtually identical to the visible absorption spectrum of iso-CF2I2 trapped in matrix isolation experiments [with subtracted I-2(X) absorption]. The formation of this isomer in solution at room temperature has direct dynamic implications for the ultrafast production of molecular iodine from electronically excited CF2I2.