MOLECULAR ABUNDANCES AND LOW-MASS STAR-FORMATION .1. SI-BEARING AND S-BEARING SPECIES TOWARD IRAS 16293-2422

Results from millimeter and submillimeter spectral line surveys of the protobinary source IRAS 16293-2422 are presented. Here we outline the abundances of silicon- and sulfur-containing species. A combination o f rotation diagram and full statistical equilibrium/radiative transfer calculations is used to constrain the physical conditions toward IRAS 16293 and to construct its beam-averaged chemical composition over a 10-20'' (1600-3200 AU) scale. The chemical complexity as judged by spe cies such as SiO, OCS, and H2S, is intermediate between that of dark m olecular clouds such as L134N and hot molecular cloud cores such as Or ion KL. From the richness of the spectra compared to other young stell ar objects of similar luminosity, it is clear that molecular abundance s do not scale simply with mass; rather, the chemistry is a strong fun ction of evolutionary state, i.e., age.