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

Abstract

2014) The ro-vibrational analysis of the v 4 fundamental band of CF 3 Br from jetcooled diode laser and FTIR spectra in the 8.3-µm region,The v 4 fundamental band of CF 3 79 Br and CF 3 81 Br, present in natural isotopic abundance, was investigated in the 8.3-μm 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 transform infrared spectrum covering 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 CF 3 79 Br, 4047 to CF 3 81 Br, with J max = K max =80; of these, 3171 for CF 3 79 Br and 2755 for CF 3 81 Br 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 C 3v symmetry. The v 4 band of both the isotopologues resulted essentially unperturbed, but the l = 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 CF 3 79 Br and CF 3 81 Br were obtained. The bromine isotopic splitting amounts to 6.9 × 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.

Computing sextic centrifugal distortion constants by DFT: A benchmark analysis on halogenated compounds

“…We performed the investigation on a set of four small semi-rigid molecules, focusing on halomethanes and haloethenes, a class of compounds which in recent years was the subjects of several theoretical and experimental investigations (see for examples Refs. [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] and references therein). For these molecules very accurate computed values are available in literature (i.e.…”