HIGH-PRESSURE RAMAN-SPECTROSCOPIC STUDY OF CYCLOHEXANE C6H12 AND C6D12

We have performed a series of detailed high-pressure Raman scattering studies on both deuterated and hydrogenated cyclohexane, C6D12 and C6H12, respectively. Our results indicate that, upon increasing pressure from ambient to roughly 30 kbar, at room temperature, both C6H12 and C6D12 exhibit three solid-solid phase transitions between phases I, III, IV, and a previously unreported phase V. At ambient pressure and low temperature, both deuterated and hydrogenated cyclohexane exist in yet another solid phase (phase II). The similarity of the Raman spectra in each phase of both compounds suggests that all of the phases contain undistorted chairlike molecules and that the major effect of deuteration is to alter the range of stability of each phase without having a significant influence on the phase diagram topology. The Raman spectra of the metastable phase in C6H12, obtained by rapid cooling of phase I at ambient pressure, has also been investigated, and it is found to be ordered and not an orientationally disordered plastic-crystal glass, as previously suggested.