Deuterated methylene iodide at high pressures: a Raman study

Raman spectra of solid CD2I2 have been recorded at ambient temperature and at pressures up to 10.45 GPa. The freezing pressure was determined to be 0.28 ± 0.14 GPa at 295 K. The resulting crystal has a structure isomorphic with that of CH2I2 grown under the same conditions but different from that adopted by CD2I2 at low temperatures. Evidence for reversible phase transitions near 2.1 and 6 GPa is presented. The wavenumber of the Ly lattice mode becomes larger than the v4 internal mode at about 3.0 GPa. At higher pressures, the intermolecular force constants for CD2I2 are larger than the corresponding ones for CH2I2 at the same pressure, probably as a result of closer packing. Analysis of an overtone band suggests that the molecular anharmonicity is essentially independent of pressure.