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,no,n*)→π* and the strong u.v. absorption as (σ,non*)→σNN*. 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 (no,n*,σNN)→π* and the strong u.v. absorption as πo→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 πo→π*.