Molecular biaxiality and reorientational correlation functions in nematic phases: Infrared spectroscopy

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Abstract
In this paper we apply the theoretical results presented in the preceding paper to the case of infrared spectroscopy. A theoretical evaluation of the correlation functions connected with spinning and tumbling molecular fluctuations and comparison with the experimental correlation functions obtained from band-shape analysis of infrared dichroic spectra in ordered nematic phases allows us to evaluate the effect of molecular biaxiality (i.e., deviations from cylindrical symmetry) on polarized ir absorption spectra. From the fitting of our data we are able to recover the ‘‘true’’ behavior of the spinning diffusion coefficients (the tumbling coefficients are not affected by molecular biaxiality as predicted by the theory) and obtain a semiquantitative estimate of the strength of the biaxial term in the nematic potential.