Far-infrared absorption in the highly ordered smectic phases of TBBA

Abstract

The far-infrared absorption of terephthal-bis-butylaniline (TBBA) in the smectic H, VI, VII and crystalline phases has been studied in the range 30-650 cm-1. Spectra of the former three phases closely resemble each other over the entire spectral range. On transforming to the crystalline phase several new modes appear, especially in the low frequency region. When compared to the Raman spectra of these phases, the present results show interesting differences which allow for further deductions in characterizing the mesophases considered here. The lineshape of bands in the range 460-510 cm-1 is seen to exhibit changes dependent upon the phase of the sample. A band centered at 476±12 cm-1 exhibits a broadening in smectic H and VI phases as compared to phase Vll. This has been attributed to the occurrence of intramolecular reorientations of the butyl chain segments in the former two phases. From a study of the half-widths (HWHM) of the band, the mean correlation time of these reorientations is estimated to be within the range of 1-2 psec.