Photodissociation of CF2ICF2I in solid para-hydrogen: infrared spectra of anti- and gauche-˙C2F4I radicals

Abstract

The photolysis of 1,2-diiodotetrafluoroethane (CF₂ICF₂I) has served as a prototypical system in ultrafast reaction dynamics. Even though the intermediates, anti- and gauche-iodotetrafluoroethyl (˙C₂F₄I) radicals, have been characterized with electron diffraction and X-ray diffraction, their infrared spectra are unreported. We report the formation and infrared identification of these radical intermediates upon ultraviolet photodissociation of CF₂ICF₂I in solid para-hydrogen (p-H₂) at 3.3 K. Lines at 1364.9/1358.5, 1283.2, 1177.1, 1162.2, 1126.8, 837.3, 658.0, 574.2, and 555.2 cm⁻¹ are assigned to anti-˙C₂F₄I, and lines at 1325.9, 1259.7, 1143.4, 1063.4, 921.0, and 765.3 cm⁻¹ to gauche-˙C₂F₄I. A secondary photodissociation leading to C₂F₄ was also observed. The assignments were derived according to behavior on secondary photolysis, comparison of the vibrational wavenumbers and the IR intensities of the observed lines with values predicted with the B3PW91/aug-cc-pVTZ-pp method. This spectral identification provides valuable information for future direct spectral probes of these important intermediates.