The Infrared Absorption Spectra of Nitrogen Dioxide and Tetroxide

The absorption spectra from 1 to 4 mu of pure NO2-N2O4 mixtures in a long tube were examined with a rocksalt and a quartz spectrometer. Several new bands were discovered from 1.9 to 4 mu in the spectra of both NO2 and N2O4. The NO2 bands were analyzed as combinations of two fundamentals. The N2O4 bands were interpreted as combinations and harmonics of reported fundamentals. Three bands of N2O4 lie at shorter wave-lengths than correspond to the work of dissociation into 2 NO2. A study of the symmetry properties shows that only those models where the NO2 groups are joined by the nitrogen atoms would give rise to the observed infrared spectrum. Some features of the spectrum seem to be in favor of the existence of molecules where the NO2 groups do not lie in the same plane.