Accurate determination of the structure of 1,3,5-trifluorobenzene by femtosecond rotational Raman coherence spectroscopy and ab initio calculations

Rotational Raman femtosecond degenerate four-wave mixing (fs-DFWM) and high level ab initio calculations are applied for the determination of the molecular structure of 1,3,5-trifluorobenzene (C6H3F3). The rotational and centrifugal distortion constants of the ground state are determined as B0=1759.410±0.004MHz,DJ=103.3±0.5Hz,DJK=-188.3±0.9Hz and DK=89.6±0.6Hz. We also measured the rotational constants Bv of the vibrations ν10,ν29/30,ν23/24 and the 2ν10 overtone levels. Combining the experimental B0 constants with the structure parameters and rotational constants calculated by the coupled-cluster CCSD(T) method allows to determine accurate equilibrium structure parameters for trifluorobenzene, e.g., re(C-C)=138.42±0.1pm,re(C-H)=107.63±0.1pm and re(C-F)=134.05±0.2pm. Due to the C-F bond polarization and rehybridization effects at the C atoms, the C-H bond lengths of trifluorobenzene are shortened relative to those of benzene by 0.4 pm and the interior angles change from 120° by plus and minus 3.4°, respectively.