An ISO view on interstellar and cometary ice chemistry

The ISO-SWS instrument offering a large wavelength coverage and a resolutio n well adapted to the solid phase has changed our knowledge of the physical -chemical properties of ices in space. The discovery of many new ice featur es was reported and the comparison with dedicated laboratory experiments al lowed the determination of more accurate abundances of major ice components . The presence of CO2 ice has recently been confirmed with the SWS (Short W avelength Spectrometer) as a dominant ice component of interstellar grain m antles. The bending mode of CO2. ice shows a particular triple-peak structu re which provides first evidence for extensive ice segregation in the line- of-sight toward massive protostars. A comparison of interstellar and cometa ry ices using recent ISO data and ground-based measurements has revealed im portant similarities but also indicated that comets contain, beside pristin e interstellar material, admixtures of processed material. The investigatio n of molecules in interstellar clouds is essential to reveal the link betwe en dust in the interstellar medium and in the Solar System.