High-resolution infrared spectroscopy of the interacting ν9, ν5 + ν6 and 3ν6 levels of CH279BrF

Abstract The high-resolution (0.0030 cm −1 ) Fourier transform infrared spectrum of CH 2 79 BrF has been studied in part of the atmospheric window between 910 and 980 cm −1 , the region of the ν 9 (935.847 cm −1 ) and ν 5  +  ν 6 (961.239 cm −1 ) bands. The ν 9 fundamental consists of a pseudo a -type band induced by Coriolis coupling with ν 5  +  ν 6 , in turn exhibiting a predominant a -type structure. Several interactions connecting these levels and the dark state 3 ν 6 have been assessed. The whole data set is treated using Watson’s A-reduced Hamiltonian in the I r representation implemented with first order a - and b - and c -type Coriolis terms. A detailed analysis of the rotational structure yields a set of accurate upper-state parameters up to quartic distortion terms for ν 9 and ν 5  +  ν 6 . In addition, spectroscopic information about the dark ternary overtone of ν 6 has been obtained.