Molecules in Bipolar Outflows
  Bipolar outflows constitute some of the best laboratories to study shock
chemistry in the interstellar medium. A number of molecular species have their
abundance enhanced by several orders of magnitude in the outflow gas, likely as
a combined result of dust mantle disruption and high temperature gas chemistry,
and therefore become sensitive indicators of the physical changes taking place
in the shock. Identifying these species and understanding their chemical
behavior is therefore of high interest both to chemical studies and to our
understanding of the star-formation process. Here we review some of the recent
progress in the study of the molecular composition of bipolar outflows, with
emphasis in the tracers most relevant for shock chemistry. As we discuss, there
has been rapid progress both in characterizing the molecular composition of
certain outflows as well as in modeling the chemical processes likely involved.
However, a number of limitations still affect our understanding of outflow
chemistry. These include a very limited statistical approach in the
observations and a dependence of the models on plane-parallel shocks, which
cannot reproduce the observed wing morphology of the lines. We finish our
contribution by discussing the chemistry of the so-called extremely high
velocity component, which seems different from the rest of the outflow and may
originate in the wind from the very vicinity of the protostar.
