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 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 v(10); v(29/30); v(23/24) and the 2v(10) 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., 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 degrees by plus and minus 3.4 degrees, respectively. (C) 2009 Elsevier B.V. All rights reserved.