The Infrared Spectra of Tetranitromethane

Cooling curve investigations show that the transition between the two crystalline forms of tetranitromethane occurs at −99.8°C and its character suggests an order‐disorder transformation. The infrared spectra of tetranitromethane were obtained at 25°C (vapor), 18°C (liquid), −40°C (solid I), −88°C (solid I), −104°C (solid II) and −126°C (solid II). The spectra of the vapor are best interpreted by a molecule with $S_4\text{−4̄}$ symmetry whereas reported Raman spectra indicate $D_2\text{d−4̄2m}$ symmetry in the liquid. Satisfactory agreement between these and the x‐ray diffraction data require molecules of both symmetries. A complete lack of selection rules was observed in the spectra throughout the solid range.