Dark Clouds are Really Dark by Dr. Edwin A. Bergin (CfA)   The dense cores of star forming molecular clouds are generally studied through the emission lines of various molecular tracers. I will present a study of the molecular gas in a core where the density profile is well described by a Bonnor-Ebert sphere near equilibrium. These observations reveal important clues to molecular core dynamics, including systematic velocity gradients, and a chemistr y that is dominated by depletion of gaseous molecules onto grain surfaces. I will outline the basic physics of the interaction between molecules and grain surfaces and show that when the physics is coupled into a chemical model there is excellent agreement between theory and observations. Finally, given the near total depletion of gaseous molecules it is entirely possible that almost all molecular species are frozen onto the surfaces of dust grains. Thus the innermost regions of dense cores, prior to the formation of a star, may be truly dark and evade detection by conventional methods of probing cores using molecular emission.