INFRARED SPECTRA OF MATRIX ISOLATED $CIF_{3}$ AND $BrF_{3}$

This work was supported by the U.S. Army Research Office, Durham, and the Advanced Research Projects Agency. $^{1}$H. Selig, H. H. Claassen, and J. H. Holloway, J. Chem. Phys. 52, 3517 (1970).""Author Institution: Department of Chemistry, Texas Technological UniversityThe infrared spectra of matrix-isolated $CIF_{3}$ and $BrF_{3}$ have been investigated in the region from $800 cm^{-1}$ to $33 cm^{-1}$. All six fundamentals have been observed in Ar and $N_{2}$ matrices for both molecules, which are of similar planar T-shape, and most of them in a Ne matrix. The two lowest frequency fundamentals, which could not be separated in the gas phase $spectra^{1}$ were clearly visible in the matrix-isolation spectra. Both molecules show only small gas-matrix frequency shifts. Multiplet structure for both molecules suspended in Ar matrices may be understood in terms of isotope and matrix site effects. Force constants were calculated for $CIF_{3}$ and $BrF_{3}$ monomers. Several absorption bands found at lower matrix isolation ratios are attributed to dimers and a tentative vibrational assignment is presented. A similar dimer structure is assumed for both substances. It seems best represented by associations through the long $X- F$ bonds: a structure also favored by the x-ray and NMR data. Comparison of the overall data for $CIF_{3}$ with that for $SF_{1}$ suggests reassignment of the axial and equatorial $S- F$ stretching vibrations for $SF_{1}$ monomer. In this way, consistent experimental agreement between these closely related molecules is achieved and a highly likely intermolecular mechanism is favored for the exchange of nonequivalent F atoms that is observed in the liquid by NMR spectroscopy