THE DISTRIBUTION OF MOLECULES IN STAR-FORMING REGIONS

A number of maps of low-mass star-forming regions have shown the molec ule CS to be more widespread than NH3, despite having a higher critica l density in the transitions in question. In a previous paper a model was presented of unresolved clumps around the star-forming core. The c lumps are transient and exhibit emission only from molecules that form quickly. In this paper it is shown how families of molecules can be f ound that ought to follow either the CS or NH3 behaviour if mapped ade quately in similar sources. The first family of early-time molecules, includes such species as CH4, CH3, H2CO, H2CS, HC3N, CN and HCN. The s econd family of late-time molecules includes the species HCO+, NO, OH, SO, N2H+, Oz, Nz and OCN. The chemistry of these molecules is discuss ed.