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

Abstract

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 ( C 6 H 3 F 3 ) . The rotational and centrifugal distortion constants of the ground state are determined as B 0 = 1759.410 ± 0.004 MHz, D J = 103.3 ± 0.5 Hz, D JK = - 188.3 ± 0.9 Hz and D K = 89.6 ± 0.6 Hz . We also measured the rotational constants B v of the vibrations ν 10 , ν 29 / 30 , ν 23 / 24 and the 2 ν 10 overtone levels. Combining the experimental B 0 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., r e ( C – C ) = 138.42 ± 0.1 pm, r e ( C – H ) = 107.63 ± 0.1 pm and r e ( C – F ) = 134.05 ± 0.2 pm . 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.