High-resolution rovibrational spectroscopy of fluorobenzene, C6H5F: analysis of the B1 fundamentals ν4, ν10b, ν17b, the B2 fundamental ν15 and assignment of the A1 levels ν12, 2ν16a and 2ν18b†

We report the rovibrational analysis of the highly resolved (instrumental bandwidth [GRAPHICS] = 0.0008-0.0018 cm(-1) full width at half maximum [FWHM]) Fourier transform infrared (FTIR) spectrum of fluorobenzene measured with our Zurich Fourier transform interferometric spectrometer prototype (Bruker IFS 125 HR ZP 2001) in the range 600-1300 cm(-1). The analysis comprised initially three B-1 bands and led to an identification of Coriolis resonances and a new assignment of three A(1) bands in the region 790-850 cm(-1). In detail, three B-1 fundamentals, nu(4) ( [GRAPHICS] cm(-1)), nu(10b) ( [GRAPHICS] cm(-1)) and nu(17b) ( [GRAPHICS] cm(-1)) have been analysed using an effective Hamiltonian. A perturbation of the B-2 fundamental nu(15) ( [GRAPHICS] cm(-1)) was detected and the interaction is interpreted as a crossing Coriolis resonance between the states nu(15) and a dark state assigned as nu(4) + nu(18b). The Coriolis parameter xi(x) was determined to be -0.00345 cm(-1). The rovibrational analysis of the region between 790 and 850 cm(-1) revealed three A(1) bands assigned to nu(12) ( [GRAPHICS] cm(-1)), 2 nu(18b) ( [GRAPHICS] cm(-1)) and 2 nu(16a) ( [GRAPHICS] cm(-1)). A Coriolis resonance between the states 2 nu(16a) and a dark state assigned as nu(10a) ( [GRAPHICS] cm(-1), A(2) symmetry) was identified and the Coriolis coupling constant xi(z) was determined to be 0.0145 cm(-1). The root mean square deviation d(rms) is in the range 0.0002 - 0.0003 cm(-1) (6-9 MHz) for the adjustment of the model to almost 17000 assigned rovibrational absorption line positions. This indicates an excellent representation of the data by the model.