High resolution FTIR spectra of¹²CF₃I,¹³CF₃I and¹²CF₃⁷⁹Br near 1050 cm^-1and 550 cm^-1

Abstract

High resolution FTIR spectra of CF3 79Br, 12CF3I and 13CF3I have been studied and analysed in the region of the v 1 CF3 symmetric stretching fundamental which is accessible to CO2-laser pumping. Spectra with a resolution of 0.01 cm-1 have been obtained at various temperatures. J clusters were resolved and analysed by polynomial and simulation methods. In 13CF3I a Fermi resonance between v 1 (v eff = 1047.60 cm-1) and 4v 6 0 (v eff = 1049·51 cm-1) has been established. For CF3 35Cl, 12CF3 79Br and 12CF3I the Fermi resonance between v 1 and 2v 5 0 has been analysed semiquantitatively. Further rotational resonances occur in 12CF3I, which could not be assigned unambiguously, but are likely to be due in part to v 3 + 3v 6. The spectra of the v 5 fundamental near 550 cm-1 have been obtained for CF3Br and CF3I at a resolution of 0·05 cm-1. Whereas v 5 appears to be unperturbed for CF3 79Br, for CF3I a Fermi resonance between v 5 and v 3 + v 6 and a rotational resonance of v 5 with 2v 6 have been assigned. A set of recommended vibrational frequencies for 12CF3I and 13CF3I is given, and several effective rotational constants and anharmonic constants including Fermi resonance are quoted. The implications of the results for the I.R.-multiphoton excitation of these molecules are discussed briefly.