Observational Evidence for the Excitation of HCN and H20 in Protostellar Molecular Clouds

Detailed modeling of the molecular cloud and excitation of HCN in the Orion Nebula have been compared with HCN observations. This results in information about the density distribution of the cloud, collisional interaction of H2 with HCN, number densities, kinetic temperature, cloud mass, upper age limit, and molecular isotopic ratios. It is found that the 1H12C14N J = 1-0 transition is not saturated and that the molecular isotopic ratios do not reflect terrestrial elemental ratios. These results are combined with VLB observations of H2O masers in Orion and detailed H2O excitation calculations of others to produce a consistent interpretation of the Orion molecular cloud. Subject headings: masers - molecules, interstellar - nebulae - Orion Nebula