High-resolution infrared spectroscopy of CH₂D⁷⁹Br: ro-vibrational analysis of the ν₄ and ν₈ fundamental bands

The high-resolution Fourier transform infrared spectrum of CH₂D⁷⁹Br has been recorded and analysed in the region of the ν₄ and ν₈ fundamentals located in the range 1125−1360 cm⁻¹. The strong ν₄ band, centred at 1225 cm⁻¹, shows an a/b-hybrid structure with predominant a-type character, whereas ν₈, at 1253 cm⁻¹, generates a c-type contour comparable in intensity to the b-type component of ν₄. The upper states of these fundamentals are coupled through a- and b-type Coriolis resonances; further complications in this band system arise from perturbations due to the ν₆ = 2 (1183 cm⁻¹) and ν₅ = ν₆ = 1 (1359 cm⁻¹) dark states. The former interacts with ν₈ = 1 by b-type Coriolis coupling, whereas the latter perturbs the ν₄ = 1 and ν₈ = 1 levels by anharmonic and a-type Coriolis resonances, respectively. Accurate upper state parameters and interaction terms have been determined for the tetrad system ν₄/ν₈/2ν₆/ν₅+ν₆ by also including in the dataset the assigned transitions of the 2ν₆−ν₆ and ν₅+ν₆−ν₆ hot bands obtained from previous analysis.