The ro-vibrational analysis of thev4fundamental band of CF3Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

The v4 fundamental band of CF3 Br-79 and CF3 Br-81, present in natural isotopic abundance, was investigated in the 8.3-m region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5-1205.0 cm-1, 1208.0-1210.1 cm(-1) and 1212.5-1214.5 cm(-1). The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm(-1). A Fourier transforminfrared spectrumcovering the entire spectral region of the v(4) band, between 1190 and 1220 cm(-1), was recorded at 298 K with a resolution of 0.004 cm(-1). The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v(4). In total, 4651 transitions were assigned to CF3 Br-79, 4047 to CF3 Br-81, with J(max)'' = K-max '' = 80; of these, 3171 for CF3 Br-79 and 2755 for CF3 Br-81 are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C3v symmetry. The v4 band of both the isotopologues resulted essentially unperturbed, but the Delta l = Delta k = +/- 2 l-resonance was found to be active within the v(4) = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v(4) = 1 for CF3 Br-79 and CF3 Br-81 were obtained. The bromine isotopic splitting amounts to 6.9 x 10(-3) cm(-1). In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.