Rotational bias of an antiferroelectric liquid crystal studied by polarized Fourier transform infrared spectroscopy

Experimental studies of the absorbance vs polarization angle of the incident ir beam on a cell have been carried out for several absorbance bands in the SmA phase and in electrically induced ferroelectric states $F(+)$ and F(-) of the SmCA* and SmC* phases of an antiferroelectric liquid crystal. The various absorbance profiles are quantitatively analyzed in terms of the rotational bias parameters of the azimuthal distribution function of the transition moments located in the core of the molecule. The parameters so determined reproduce the profiles of the other transition dipole moments. The parameters of the distribution function for the rotational motion around the long molecular axis show the predominance of the quadrupolar bias relative to the polar bias in both SmC* and SmCA* phases, while a significant quadrupolar bias is also seen in the SmA phase.