INFRARED STUDY OF PHASE-TRANSITION AND CHEMICAL-REACTION IN TETRACYANOETHYLENE UNDER HIGH-PRESSURE

Infrared spectra of the cubic and the monoclinic phases of tetracyanoethylene have been investigated as a function of pressure at room temperature. The cubic phase, a low-temperature phase stable below 318 K at ambient pressure, appeared to be stable up to 6 GPa. The high-temperature monoclinic form metastably obtained at room temperature showed a structural transformation near 3 GPa. This high-pressure phase, showing an infrared spectrum different from that of the cubic phase, transformed reversibly to the monoclinic phase on unloading. Polymerization occurred in both the cubic and high-pressure molecular phases near 6 GPa.