Analysis of the rotationally-resolved infrared spectrum of CD₃⁷⁹Br and CD₃⁸¹Br between 900 and 1400 cm⁻¹

The infrared spectrum of CD₃⁷⁹Br and CD₃⁸¹Br between 900 cm⁻¹ and 1400 cm⁻¹ has been analyzed at high resolution. In this region, two fundamental vibrational states, v₂ = 1 and v₅ = 1, an overtone state, v₃ = 2, and a combination state, v₃ = v₆ = 1, have been analyzed for both isotopologues. As found in other halomethane molecules, strong Coriolis resonances couple the v₂ = 1 state to the v₅ = 1 state, and similar resonances were also used to describe the coupling found between the v₅ = 1 state to the v₃ = 2 state. A new determination of the K-dependent constant A₀ was performed for each isotopologue through the use of perturbation-allowed transitions. The values for A₀ determined from the analysis are 2.6001898(26) and 2.6001905(27) for CD₃⁷⁹Br and CD₃⁸¹Br, respectively. Density functional theory calculations were performed to examine the efficacy of high-level theoretical calculations to accurately predict spectroscopic constants. The density functional theory calculations had variable success with the largest errors associated with the prediction of the ΔB rotational constants of the interacting states.