Institut d'Astrophysique Spatiale, Orsay, France
With its large wavelength coverage and its spectral resolution
adequate for solid state features, ISO is a unique tool not only to
identify and quantify simple abundant molecular species in the form of
``dirty ices'' but also to study some of the physico-chemical properties of
these ices. Various icy molecules such as H2O, CO, CO2, CH3OH,
H2CO are
detected, for the first time in their various fundamental bands in the mid
infrared spectral region. In some cases, the exact peak position,
bandwidths and band structures of the identified molecules allow to
unravel the degree of mixtures of the various ice components and to study
the formation of molecular complexes such as the complex
.
These
effects will be reviewed in line with recent ISO results. It will be shown
that laboratory simulations involving IR spectroscopy of calibrated ice
films allow to duplicate exactly most of the observed features. Solid state
effects completely dominate over grains shapes effects, for the
interpretation of the infrared spectra in the mid-infrared region.
Finally, the merging of SWS and LWS spectra allows the detection of the transverse optical phonon mode of the ice (the 44 micron band) in absorption and reveals the intrinsic limitations of the comparison between laboratory and astronomical spectra in the far-infrared where complex radiation transfer effects must be taken into account before comparing laboratory and astronomical spectra.