Infrared spectra of the CF3I dimer: a concurrent application of matrix-isolation spectroscopy and cavity ring-down...

We have observed infrared spectra of the CF(3)I dimer produced in a supersonic jet by matrix-isolation Fourier transform infrared spectroscopy and infrared cavity ring-down (IR-CRD) spectroscopy. In the matrix-isolation experiments, the dimer was isolated in an Ar matrix by the pulse-deposition method. The recorded spectral range covers the symmetric (nu(1)) and doubly degenerate (nu(4)) C-F stretching regions. From the concentration dependence of the matrix-isolation spectra we have assigned one dimer band for each fundamental region. It was not easy to identify the dimer band for the nu(4) band because of the multiplet feature of the monomeric nu(4) band caused by the site symmetry breaking. The spectra of (CF(3)I)(2) in the nu(4) band region were thus also measured in the gas phase by IR-CRD spectroscopy, where we detected two dimer bands. Comparing the observed band positions with the results of quantum chemical calculations, we have assigned the observed dimer bands to the head-to-head isomer. The structure of (CF(3)I)(2) and its photochemical implications are discussed, in comparison with methyl iodide dimer reported previously [Ito et al., Chem. Phys. Lett. 343, 185 (2001)].