LAUSR

Abstract The ν3 parallel, and ν6 perpendicular infrared-active vibrational bands have been analyzed for both CD379Br and CD381Br at 0.0015 cm-1 resolution. The band origins for the v3 = 1 state are 577.28925(2) cm-1 and 575.97685(2) cm-1 for the CD379Br and CD381Br isotopologues, respectively; for the v6 = 1 state the band origins are 713.46997(1) cm-1 and 713.38156(1) cm-1, respectively. The v3 =1 and v6 =1 vibrational states are possibly the only unperturbed vibrational states in CD3Br, and thus yield the most reliable infrared spectroscopy-based determination of the ground state rotational constants. The spectroscopic constants for both vibrational states, as well as the ground vibrational state were improved compared to previous studies through a direct fit of the vibrational bands, as well as a separate fit of the ground state combination differences. Ab initio calculations were performed to examine the efficacy of high-level theoretical calculations to accurately predict spectroscopic constants. Though not used in fitting the experimental data, nuclear quadrupole hyperfine splitting by the bromine atoms was observed in both vibrational states, an uncommon observation in the infrared spectra of polyatomic molecules.