Obliquely projecting chiral alkyl chains and their precession around the long core axes in the smectic-Aphase of an antiferroelectric liquid crystal

By deuterizing the chiral and achiral alkyl chains separately, we have observed the ir absorbance vs polarizer rotation angle for the C${\mathrm{H}}_2$ and phenyl ring stretching peaks in a prototype antiferroelectric liquid crystal, 4-(1-methylheptyloxycarbonyl) phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC). The angle between the chiral chain and core axes is more than 54.7° (the magic angle) even in the smectic-$A$ (Sm-$A$) phase and the precession appears to be biased or hindered toward the tilt-plane normal in the chiral smectic-$C$ (Sm-$C^{*}$) phase.