Raman spectra and phase transition of the phenothiazine crystal

摘要: Abstract Polarized Raman spectra of single crystals phenothiazine which undergoes a phase transition around 250 K and is ferroelastic in the low-temperature were measured lattice-vibrational region for temperatures ranging from 89 to 300 K. The high- phases obey selection rules required orthorhombic monoclinic structures, respectively. Anomalous temperature dependences are observed frequency, intensity linewidth band appearing lowest-frequency region. This attributed mainly librational motion molecule, important evaluation this transition. A gradual change molecular orientation inferred occur over wide interval along vibrational coordinate above libration. Another strong, low-frequency band, characteristic spectra, suggested arise mixing between intramolecular lattice vibrations. mode considered play some role too. interaction optical modes acoustic briefly discussed connection with ferroelasticity phase. depends on quality specimen; correct found be 248.8 slightly lower than previously reported value.