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Fourier transform infrared (FTIR) spectra of nitrogen dioxide layers deposited at various rates and substrate temperatures, are reported. Bands assignable to N2O4(D2h) (ordered and disordered layers), to O=N–O–NO2 ‘‘D’’ and ‘‘D′’’ isomers, to NO+NO−3 nitrosonium nitrate and to the NO2 monomer were observed. The relative amounts of species depends upon deposition conditions. Temperature cycling effects were followed up to 205 K. Solid N2O4(D2h) behaves like a normal, stable molecular solid, its disordered layer exhibiting small frequency shifts, but also being stable with respect to temperature cycling. The observation of NO+NO−3 bands is related to the existence of the D′ isomer and of monomeric NO2. Raman experiments overemphasize the NO+NO−3 form due to resonant enhancement.

Solid layers produced by the deposition at cryogenic temperatures of Ar-H,O-CO and of CO-H,O mixtures have been investigated by FTIR spectroscopy. Effects of variations in concentration ratios, in deposition temperature and of temperature cycling were studied. It is possible to assign all observed bands to single-component and to mixed (CO),(H,O), complexes. For the production of mixed species, higher deposition temperatures are more effective than temperature cycling. Formation is due more to H,O than to CO surface migration. Conclusions were applied to a previous study of porous ices produced by temperature cycling of noble gas-H,O solid mixtures onto which CO was deposited as a probe. They confirm that porous ices from Ar-H,O mixtures consist of small clusters with 'surface porosity' and a large proportion of dangling OH bonds. The CO gets attached to more than a single OH bond. Ice so formed from Ne-H,O mixtures has 'bulk porosity' with scattered free OH bonds. Deposited CO penetrates it and forms small solid-like clusters or bonds to single OH bonds.