Interstellar ices are an important dust component inside dense
 molecular clouds. The abundance of carbon-bearing molecules in ice
 mantles is not well known because the important molecules CO2 and CH4
 cannot be observed from the ground. Observations of solid CO (see
 fig.1 in Appendix A) reveal that interstellar ices consist of
 different components: H2O-rich ices as well as ices dominated by
 non-polar molecules such as CO, CO2, or CH4. These distinct components,
 often associated with the same star, may result from outgassing of the
 highly volatile, non-polar molecules near protostars or from the
 predominance of different chemical routes at different times during
 the collapse or in different spatial zones around the protostar.
 Understanding the influence of protostars on the composition of their
 natal molecular clouds is a key problem within astrophysics. A better
 understanding of the abundances of organic molecules in interstellar
 ices around low mass protostars will also lead to a better
 understanding of the organic inventory of comets and the outer ice
 planets and satellites in our solar system.

 Using the SWS, we propose to study the solid CO2 and CH4 bands, which
 can not be done from the ground due to telluric CO2 and CH4 absorption.
 In combination with ground based CO and CH3OH data, we can then
 determine the abundances of the dominant carbon-bearing molecules in
 interstellar ices.  The peak position and profile of the solid CO2 and
 CH4 bands are sensitive to the solid state environment of these
 molecules and detailed comparison with laboratory profiles yields
 therefore additional, independent constraints on the non-polar ice
 composition (see figs.2 and 3 in Appendix A).  Finally, because of
 their different chemical formation routes and volatility, solid CO2
 and CH4 studies allow direct tests of existing models for the origin
 of non-polar versus H2O-rich ices.