Chemical studies have a great potential to study the structure and evolution of the bipolar molecular outflows driven by young stellar objects. In this paper, we discuss some very recent mm-wave studies of L1157, a bipolar molecular outflow driven by a Class 0 protostar. These observations are very useful to illustrate the chemical alterations produced by a violent highly-collimated outflow. Different molecular lines are observed to trace different components of the gas. Some molecules are abundant in the quiescent medium but are not observed in the shock (e.g. C$_3$H$_2$, N$_2$H$^+$, H$13$CO$^+$, DCO$^+$), whereas some otherwise rare molecules are very enhanced at the shocked region (e.g. SiO, CH$_3$OH, H$_2$CO, HCN, CN, SO, SO$_2$). In addition, we have observed strong gradients in the chemical composition across the outflow blue lobe. We briefly discuss the chemistry of the most important molecules, devoting special attention to the species which are thought to be abundant in interstellar ice mantles.
Herbig-Haro Flows and the Birth of Stars
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