  We present a detailed model for the thermal balance, chemistry, and radiative
transfer within quiescent dense molecular cloud cores that contain a central
protostar. Large variations in the gas temperature are expected to affect the
gas-phase chemistry dramatically; with the predicted H2O abundance varying by
more than a factor of 1000 within cloud cores. Based on our predicitions for
the thermal and chemical structure of the cores, we have constructed
self-consistent radiative transfer models to compute line strengths and
profiles for transitions of various isotopomers of CO, H2O, and OI. We predict
the high lying transitions of water to be in absorption, and low gain maser
emission at 183 GHz. We predict the 63 micron line of OI to be in absorption
against the continuum for many sources. Finally, our model can also account
successfully for recent ISO observations of absorption in rovibrational
transitions of water toward the source AFGL 2591.
