A Raman spectroscopic study of the low-frequency vibrations in anisole and anisole- d3

Abstract

Low-frequency Raman spectra of solid anisole and of solid anisole- d 3 have been recorded at 130 K. The phenyl torsion observed at 148 cm −1 is shifted to 133 cm −1 upon deuteration of the methyl group. The twofold torsional barriers calculated from these frequencies are 4033 ± 110 cm −1 and 4094 ± 123 cm −1 indicating that coupling to other low-frequency modes in both cases is of the same order of magnitude. The methyl torsional mode was observed at 285 cm −1 in the spectrum of solid anisole and at 183 cm −1 in the spectrum of anisole- d 3. The threefold barriers calculated using these frequencies are 1847 ± 20 cm −1 and 1465 ± 18 cm −1 respectively. These barrier values indicate that the methyl torsion is coupled to another low-frequency mode. A doublet centered at 230 cm −1 in anisole is shifted to 245 cm −1 in anisole- d 3; it is proposed that this is due to a ring mode coupled to the methyl torsion. The splitting is interpreted as an example of Davydov splitting.