Chemistry behind interstellar shocks

Molecular gas in the Galaxy is subject to frequent shocks due to numerous processes, both external (e.g. the impact of an expanding supernova blast wave) and internal (e.g. outflows from embedded young stars). Shocks affect the chemical abundances profoundly, either as a result of molecular synthesis behind a slow shock or as a result of molecular dissociation behind a faster shock. Recent work on interstellar shock chemistry reviewed here includes (1) the chemistry behind dissociative shocks, (2) the role of polycyclic aromatic hydrocarbons in the structure of shocks in postshock chemistry, and (3) the postshock fractionation of deuterium in species such as DCO+, DCN, and HDO. The success of shock models in explaining observed abundances in the well-studied regions OMC 1 and IC 443 will be addressed