Terahertz spectroscopy of the crystalline α-quaterthiophene: A combined experimental and density functional theory study

We have investigated the experimental terahertz phonon modes in a model oligothiophene, the α-quaterthiophene (LT phase), by using infrared and inelastic neutron scattering spectroscopy in the 10–50 cm−1 (0.3–1.5 THz) domain. The ability of density functional theory to reproduce the terahertz infrared phonon modes is also reported. In agreement with the calculation, the experimental infrared spectrum at 10 K is dominated by two phonon modes centered at 32 and 46 cm−1 respectively assigned to an antiphasis translation mode and a libration of rings.