The dimeric nitrogen oxides. Part I. Electronic absorption of the nitrogen oxide dimer, and comparison of observed and calculated spectra for dinitrogen dioxide, trioxide, and tetraoxide

Abstract

The spectrum of liquid nitrogen oxide. NO, in the visible and near-i.r. region is reported. Nitrogen oxide in condensed phases is colourless, and the colours commonly reported are due to contamination, notably with dinitrogen trioxide. Reasonable agreement has been found between the electronic absorption measured for dinitrogen dioxide, N₂O₂, trioxide, N₂O₃, and tetraoxide, N₂O₄, and the transitions predicted by the CNDO/S method of Del Bene and Jaffe. For N₂O₂ this describes the near-i.r. band as (σ,n_o,n*)→π* and the strong u.v. absorption as (σ,n_on*)→σ_NN*. The low energy of the magnetically active transition probably accounts for the feeble paramagnetism of the dimer molecule. For N₂O₃ the visible-absorption band is given as (n_o,n*,σ_NN)→π* and the strong u.v. absorption as π_o→π*. For N₂O₄ the two fairly weak u.v. bands are calculated as n*→π* and π*→σ* respectively, and the strong u.v. band as a mixture of n*→σ* and π_o→π*.