Correlation field splitting of intramolecular vibrations of crystalline tetracene in terahertz region

The temperature dependence of terahertz (THz) absorption was observed for molecular crystals of tetracene using the Fourier transform infrared (FT-IR) spectroscopy. Over the frequency range of 1 to 6 THz (33 to 200 cm-1), THz absorptions corresponding to phonon and intramolecular vibrational modes were confirmed. Furthermore, the intramolecular vibrational modes exhibited correlation field splitting that originated from crystallization. A temperature-induced phase transition was successfully detected for the intramolecular vibrational modes of tetracene, even in powder form. Our results showed that these THz absorptions are highly sensitive to the molecular orientations within the crystal.