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.