The electronic absorption spectra for NO2-N2O4 mixtures has been measured in various non-polar and polar solvents. In non-polar solvents the spectra is very similar to NO2-N2O4 mixtures in the gas state. However, in solvents with unshared electron pairs available particularly ethers, esters, ketones and tertiary amines, a complex multi-banded spectra is observed at room temperature. This spectra appears to be characteristic of NO2-N2O4 in those solvents and to be the result of the same electron donor-acceptor type molecular complexes reported previously in the literature at lower temperatures in the solid state. In olefins and n-alkyl amines reactions occur and the products formed are discussed. (Author)