Matrix-isolation IR spectra of iodotrifluoroethylene (C₂F₃I)

The infrared spectra of iodotrifluoroethylene (ITFE) recorded under matrix-isolation (MI) conditions in para-hydrogen, neon and argon were investigated. The experimental spectra were analyzed by comparison with computed anharmonic spectra obtained in the second-order vibrational perturbation theory (VPT2) framework at the MP2 and revDSD-PBEP86-D3BJ levels of theory. In para-hydrogen and neon matrices, the experimentally observable bands in the range of 1800-650 cm^-1 could be assigned to vibrational transitions of monomeric ITFE. The spectral resolution even allowed assignments of transitions arising from ¹³C-isotopologues and the observation of various higher-order resonances in the range up to ∼3550 cm^-1. A comprehensive series of MI experiments in argon obtained by varying several experimental parameters revealed a dependence of the spectra on the deposition temperature. The spectra generally showed strong site-splitting effects due to the existence of different local environments around the ITFE molecule. Detailed analysis of the experimental spectra resulted in the identification of bands which are differently affected by matrix annealing. This observation led to the conclusion that ITFE occupies two major matrix sites of different stability. Calculations on ITFE dimers confirmed that spectral changes during annealing are due to the formation of dimers, which are stabilized through π-π interactions.