Ro-vibrational analysis of the ν9 and ν16 bands of R152a

High-resolution Fourier transform infrared (HR-FTIR) spectra of R152a (CH3CHF2) at room temperature were recorded at an unapodized resolution of 0.0019 cm−1, and the fundamental bands ν9 (868.7 cm−1) and ν16 (941.7 cm−1) analysed. Transitions were assigned with the aid of Loomis-Wood plots and data fitted with Pickett's SPFIT. The a-type ν9 band is essentially unaffected by resonances, whilst the b-type ν16 band shows distinct avoided crossings affecting a number of levels. These perturbations have been treated by explicit inclusion of interacting “dark” states with suitable Coriolis parameters in the fit of ν16 transitions. Rotational levels of υ16 = 1 in the vicinity of Kc = 17 are perturbed via an a-axis Coriolis resonance with a state originating at 937.9 cm−1, identified as υ11 = 2. The levels around Kc = 47 are perturbed by a b-axis Coriolis resonance with the combination state υ10 = 1; υ17 = 1 at 951.6 cm−1.