The molecular structure of a partly deuterated chiral smectic liquid crystal 4-(I-methylpentyloxycarbonyl) phenyl 4′-octyloxybiphenyl-4-carboxylate (acronym M5POBC-d25) in a homogeneously aligned sample is studied using polarized Fourier-transform infrared (FTIR) spectroscopy. The relative orientations of the chiral and deuterated achiral alkyl chains of molecules with respect to their long axes and some properties of the orientational distributions of the carbonyl groups are quantitatively analysed for the ferroelectric SmC* phase with a field unwound structure. The analysis is carried out in terms of the absorption anisotropy of several bands related to stretching vibrations of the phenyl C6H4 fragment, the deuterated biphenyl C 12D8 fragment, two carbonyl groups situated in different parts of a molecule, the methylene groups CH2 and CD2-It has been found that the chiral and achiral alkyl chains make substantially different angles (∼60° and ∼36°, respectively) with the molecular long axis. The rotational orientational distribution of the carbonyl groups about the molecular long axes has been found to have a comparatively low polar biasing.