Molecular abundances in OMC-1 - The chemical composition of interstellar molecular clouds and the influence of massive star formation

The chemical composition of the various regions in the core of OMC-1 is investigated based on millimeter-wave spectral line survey results. The cool and extended quiescent ridge gas is characterized by fairly simple carbon-rich species whose abundances are similar to those found in other well-studied objects like TMC-1 and Sgr B2. Its chemical composition is reasonably well predicted by purely gas phase ion-molecule reaction networks. Abundances in the high-velocity plateau are dominated by outflow from IRc 2. The hot core is interpreted as a particularly large and dense clump or clumps of gas left over from the formation of IRc 2. The production of complex oxygen-rich species such as CH3OH in the compact ridge is accomplished by radiation association reactions between smaller molecular ions in the quiescent cloud material and highly abundant neutral species such as HCN and H2O supplied by the outflow from IRc 2.