Low Energy Phase Transitions in Molecular Crystals and Raman Spectroscopy: The Case of Benzil

Abstract

The low-energy phase transition discovered by Esherick and Kohler in solid benzil has been studied by Raman spectroscopy as a function of temperature and pressure. Some of the frequency shift curves exhibit a discontinuity in their slopes at the transition point, but the most striking feature is the continuous increase of the intensity of a Raman line lying at 47 cm⁻¹ when decreasing temperature or increasing pressure, followed by an intensity jump of the same line at the transition. Starting from these observations, a mechanism for the phase transition is proposed.