Modelling the anharmonic and Coriolis resonances within the six level polyad involving the ν4 fundamental in the ro-vibrational spectrum of vinyl fluoride

The Fourier transform infrared (FTIR) spectrum of vinyl fluoride, H2CCHF, has been deeply investigated in the ν4 band region around 6 μm at a resolution of 0.002 cm−1. This normal mode, of A′ symmetry species and corresponding to the CC stretching motion, yields an a/b hybrid band with a prevalent a-type character. In the present contribution, a systematic investigation is carried out by explicitly taking into account the strong and invasive anharmonic and Coriolis resonances, which perturb all of the ν4 ro-vibrational states. Indeed, the ν4=1 state is involved in a six-level resonant polyad, which, besides ν4 (1656.0 cm−1), comprises the A′ symmetry vibrational states ν7+ν9 (1635.5 cm−1), ν10+ν12 (1641.8 cm−1) and 2ν11 (1733.6 cm−1), as well as the ν8+ν12 (1638.7 cm−1) and 2ν9+ν12 (1683.8 cm−1) combination bands of A″ symmetry. The ro-vibrational analysis led to the assignment of more than 2100 transitions of ν4 with J″≤57 and Ka″≤16, and about 1000 ro-vibrational transitions (J″≤47 and Ka″≤11) reaching the ν7=ν9=1 state. 505 transitions of these belong to the ν7+ν9−ν9 hot band, which is located at about 1052.4 cm−1 within the atmospheric window. No features are detected for the remaining vibrational states involved in the polyad, which therefore behave as dark states. By adopting an interaction model involving fourteen different anharmonic and Coriolis resonances, the assigned transitions are simultaneously fitted within the Watson's A-reduction Hamiltonian in the Ir representation up to the sixth power of angular momentum operators. As demonstrated by spectral simulations, the obtained ro-vibrational Hamiltonian well reproduces the ro-vibrational spectrum of vinyl fluoride in the 6 μm region.

► High resolution FTIR spectrum of vinyl fluoride in the region around 1650 cm−1. ► Strong interacting six level polyad involving ν4/ν7+ν9/ν8+ν12/ν10+ν12/2ν9+ν12/2ν11. ► Assigned more than 3000 ro-vibrational transitions belonging to ν4 or ν7+ν9. ► Transitions fitted within an interaction model involving Coriolis and anharmonic resonances. ► Global ro-vibrational Hamiltonian providing reliable spectral simulations.