Raman study of the phase transition in the CT-crystal anthracene-TCNB

Abstract

The Raman spectra of the CT‐crystal anthracene‐TCNB are investigated in the temperature range between 10 and 300 K. The orientational phase transition of the crystal at 206 K is observed from the temperature dependence of the resonance frequencies, intensities, and linewidths. It is shown that the low‐temperature structure is ordered and that a superstructure is formed. An assignment of some modes on the basis of isotropic shift and preresonance enhancement data is presented. Especially the frequencies of those anthracene librations are given, that are involved in the phase transition. The most intense line in the spectrum is attributed to a translational motion along the normal coordinate nearly parallel to the stack axis.

Mini-Excitons and Lattice Dynamics in Mixed CT-Crystals: An ESR, Optical and Raman Spectroscopical Study

“…This analogous behaviour is observable in the Raman spectra, too. A new mode appears at the transition temperature, and its linewidth exhibits a similar dependence on temperature as the corresponding mode of Anth-TCNB [13]. This is demonstrated in Fig.…”

Pretransitional dynamics of the structural phase transition in anthracene-TCNB: A comparison of Raman-scattering and inelastic-neutron-scattering experiments

“…A number of experimental studies have been carried out on this material using x-ray-diffraction 2-4 electron-paramagnetic-resonance ͑EPR͒ spectroscopy, 5 Raman-scattering spectroscopy, 6,7 and more recently Brillouin-scattering spectroscopy. 8 Results of these measurements have led to some controversy about the nature of the dynamical regime of the SPT.…”

“…This conclusion was favored by the absence of any soft phonon observation in the low-frequency part of the Raman spectra. 6 However, another more recent Raman study performed on oriented single crystals of high optical quality has revealed the existence of a soft optical mode ͑SM͒. 7 This mode has seemed to vanish about 15 K below the transition temperature (T c ).…”