High resolution Raman spectroscopy of gases with laser sources. VI. The rotaitional spectra of 1,3,5‐trifluorobenzene and hexafluorobenzene

Abstract

AbstractThe pure rotational Raman spectra of 1,3,5‐trifluorobenzene and hexafluorobenzene have been photographed under high resolution using a single mode argon laser as the exciting source. The observed spectra consist of sharp, highly symmetric lines which form well developed R‐ and S‐branches. The analysis of the spectra was performed on the basis of the theory of the non‐rigid, symmetric top rotor. The following ground state constants were determined. For 1,3,5‐trifluorobenzene, Bo = 0.0586517 ± (5 × 10−7) cm−1 and Dj = (1.89 ± 0.04) × 10−9 cm−1; for hexafluorobenzene, Bo = 0.0343165 ± 9 × 10−7 cm−1 and Dj = (0.70 ± 0.04) × 10−9 cm−1. The CF bond lengths for these molecules were determined by assuming the values of the carbon ring parameters of benzene. The CF bond lengths (r0‐values) of 1,3,5‐trifluorobenzene and hexafluorobenzene are then, respectively, 1.304 Å and 1.321 Å. These values are in good agreement with the CF bond lengths determined by means of the electron diffraction technique.