High-resolution infrared spectrum of CHD₂⁷⁹Br: ro-vibrational analysis of the ν₅ and ν₉ fundamentals

The high-resolution infrared spectrum of CHD₂⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 700–900 cm⁻¹ at an unapodized resolution of 0.0035 cm⁻¹. This spectral region is characterised by the absorptions of the ν₅ (814.5185 cm⁻¹) and ν₉ (716.9649 cm⁻¹) fundamental bands, corresponding to H–C–Br deformation and CD₂ rocking modes, respectively. The ν₅ vibration of symmetry species A′ gives rise to an a-/c-hybrid band with a predominant a-type component, while the ν₉ mode of A′′ symmetry produces a b-type envelope. The spectral analysis resulted in the identification of 5290 (J′ ≤ 63 and K_a′ ≤ 13) and 1657 (J′ ≤ 53 and K_a′ ≤ 12) transitions for ν₅ and ν₉ bands, respectively. The assigned data were fitted using the Watson’s S-reduced Hamiltonian in the Ir representation and the v₅ = 1 and v₉ = 1 state parameters up to the quartic centrifugal distortion terms have been obtained. From spectral simulations the dipole moment ratio |Δμ_a/Δμ_c| of the ν₅ band has been determined to be 1.4 ± 0.1 while the intensity ratio between ν₅ and ν₉ fundamentals has been estimated to have a value of 4.3 ± 0.5.