The Chemistry of Dark Clouds: New Astrochemical Tools for Star Formation   Studies
  The past decade has led to significant improvements in our understanding of the physical structure of the molecular cores of cold dark clouds. Observational efforts, in combination with improved knowledge of cloud structure, now provide clear evidence that the chemistry of dark clouds is dominated by the depletion of gaseous species onto grain surfaces. We outline the basis of these observational efforts and show how the abundance determinations have moved beyond single point analyses to the derivation of abundance profiles. We discuss the basic physics of the interaction between molecules and grain surfaces and show that when physics is coupled into a chemical model there is excellent agreement, for a limited set of species, between theory and observations. We discuss our improved understanding of cloud chemistry can be used as a new tool for studies of the formation of stars and planetary systems. 
Edwin A. Bergin