Infrared Spectrum of Crystalline CH2Cl2 and CD2Cl2. Polarization Measurements and Crystal Structure

The infrared spectra of crystalline CH₂Cl₂ and CD₂Cl₂ were measured at temperatures ranging from 5 to 125°K and at 85°K, respectively, between 5000 and 200 cm⁻¹. Splitting into two or more components was observed for several fundamentals. The mixed-crystal technique was used to prove the origin of the observed splittings, and the isotopic shifts for ³⁷Cl and ¹³C as well as the factor-group splittings were identified. These data, together with polarization measurements on polycrystalline-oriented films, relative intensity measurements, and other independent data, such as crystal density and Raman spectrum, were used to determine the crystal structure. The data accumulated are consistent with an orthormbic $D_{\text{2h}}^{14}\mathrm{(Pbcn)}$ unit cell with four molecules located on $C_2$ sites.