Smectic B liquid-crystalline glass (at 77 °K) as seen by the Mössbauer effect of Sn-bearing solute molecules

By observing the orientation dependence of the recoil-free fraction for three Sn-bearing solute molecules, we have determined the lattice contribution of a smectic B glass (at 77 ^∘{}K) to the anisotropy of the nuclear vibrational amplitude for the Sn-119 nucleus. The measured anisotropy depends on the solute shape and length and is explained in terms of the layered smectic structure and the difference between the character of the central core and the end-chain regions of the host liquid-crystal molecules. The resonant line position for the solute, 4-trimethyl-tin-benzylidene-4{'}-n-butylaniline (Sn-BBA), was found to be dependent on the angle (θ) between the preferred direction of the aligned liquid-crystalline glass and the M\"ossbauer γ beam. We interpret this in terms of an unresolved quadrupole splitting (ΔEQ) for this molecule. The line-shift data are shown to yield the sign of Vzz and the magnitude of ΔEQ for the Sn-BBA molecule.