The ro-vibrational analysis of the v₄ fundamental band of CF₃Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

Abstract

The v₄ fundamental band of CF₃⁷⁹Br and CF₃⁸¹Br, 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 v₄ 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 v₄. In total, 4651 transitions were assigned to CF₃⁷⁹Br, 4047 to CF₃⁸¹Br, with J″_max = K″_max=80; of these, 3171 for CF₃⁷⁹Br and 2755 for CF₃⁸¹Br 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 v₄ band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v₄ = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v₄ = 1 for CF₃⁷⁹Br and CF₃⁸¹Br 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.

Keywords:

• CF₃⁷⁹Br
• CF₃⁸¹Br
• Halon 1301
• jet-cooled diode laser spectroscopy
• infrared spectroscopy

Acknowledgements

The authors E. Canè, M. Villa, F. Tamassia and R. Tarroni thank Prof. Giandomenico Nivellini for recording the FTIR spectrum and Prof. Luciano Fusina for critical reading of the article. The author N. Tasinato thanks University Ca’ Foscari Venezia for his postdoctoral positions.

Additional information

Funding

The authors acknowledge the financial support of the Ministero dell’Istruzione dell’Università e della Ricerca (PRIN 2009 ‘Spettroscopia molecolare per la Ricerca Atmosferica e Astrochimica: Esperimento, Teoria ed Applicazioni’).