抄録
The second- and fourth-order orientational order parameters of the core part of the molecule, <P_2>_<app> and <P_4>_<app>, have been measured by polarized vibrational Raman spectroscopy for a homogeneously aligned ferroelectric smectic liquid crystal with three dimethyl siloxane groups in the achiral alkyl terminal chain, which shows the de Vries-type phenomena ; very large electroclinic effect in the smectic-A (Sm-A) phase and a negligible layer contraction at the phase transition between the Sm-A and Sm-C^* phases. The orientational order parameters of the rigid core part of the molecule are extremely small both with and without the external electric field in Sm-A ; <P_4>_<app> is only approximately 0.1 while the apparent tilt angle reaches at 32° when a sufficiently high electric field is applied to the cell. This result indicates that the core part is tilted by 26-36° relative to the molecular rotational long axis, although the polarized Raman spectroscopy alone could not decisively prove the existence of the de Vries Sm-A phase.
