A deuteron NMR study of the molecular dynamics of 4-n-octyloxy-4'-cyanobiphenyl (8OCB) in the mixture of 72 wt % of 8OCB and 28 wt % of 4-n-hexyloxy-4'-cyanobiphenyl is presented. The mixture has the same composition as the one used before (Shen and Dong, 1998) except in the deuteration of the component molecule. The deuteron Zeeman and quadrupolar spin-lattice times and quadrupolar splittings were measured in the nematic, smectic A, and reentrant nematic phases at 15.1 and 46 MHz. The additive potential method was employed to construct the potential of mean torque based on the observed splittings. The spectral density data from the relaxation times were interpreted in terms of the internal conformational motions of the chain decoupled from the molecular small-step rotational diffusion and the order director fluctuations. The latter motion was found to be essential to the fit of experimental results in the nematic phase. The fitting parameters obtained using a global target fitting method are acceptable when compared with those obtained from other deuteron and proton NMR studies of the same mesophases.