Thermal Processing of o -Terphenyl: A Raman Study

Abstract

Raman spectra from o-terphenyl sealed in glass capillary tubes were acquired over temperatures ranging from 233 K to 343 K. Over this temperature range, o-terphenyl can exist in the solid-crystalline, molten, supercooled-liquid, and amorphous-glassy states. Representative structure-sensitive spectra are presented along with a qualitative description. The lattice spectral feature occurring at a Raman shift of 123 cm⁻¹ displays abrupt changes in profile and intensity as melting and glass transition occur. The intensity ratio of the C-C stretching 996-cm⁻¹ line and C-H stretching line at 1008 cm⁻¹ displays a change related to the transformation of the ordered-crystalline phase to the disordered-liquid or glassy state. At a Raman shift of 1162 cm⁻¹ the solid-crystalline state shows a splitting due to the effect of the crystal field. The possibility of using these structure-sensitive Raman characteristics for in situ diagnostics during materials processing is discussed.