Reinvestigation of the Structure of Dinitrogen Tetroxide, N2O4, by Gaseous Electron Diffraction

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Abstract
A reinvestigation of the structure of N2O4 in the gas phase at −21oC has given results in good agreement with an earlier study so far as the molecular shape is concerned, but the size of the molecule appears to be about 0.9% larger than originally thought. The results for the coplanar (D2h symmetry) model are: rNN = 1.782 Å (0.0083), rNO = 1.190 Å (0.0018), ∠ ONO = 135.4o (0.58), lNN = 0.0816 Å (0.0178), lNO = 0.0381 Å (0.0019), lo1o2 = 0.0493 Å (0.0040), lN···O = 0.0729 Å (0.0061), lo1o1′ = 0.0970 Å (0.0167), and lo1o2′ = 0.0730 Å (0.0114). These distances and root-mean-square amplitudes are ra and la values; the parenthesized values are 2σ and include estimates of systematic error. The −NO2 groups have a structure very similar to that of NO2 itself. The very long N–N bond and its large amplitude of vibration imply a weak link and are in accord with the low dissociation energy.