TURBULENT-DIFFUSION AND ITS EFFECTS ON THE CHEMISTRY OF MOLECULAR CLOUDS

Turbulence in molecular clouds is well recognized, but the resultant d iffusive transport and its effects on the chemical structure of the cl ouds have not been extensively investigated. We present in this articl e a study using the mixing-length approximation of the effects of turb ulent diffusion on the chemical structure of a representative dark mol ecular cloud. With a diffusion term in the continuity equation for eac h species, we model the time-dependent gas-phase chemistry in a dense molecular cloud with fixed density and temperature profiles. We estima te the diffusion coefficient based on the observed turbulence in molec ular clouds and find that diffusive processes significantly modify the predicted chemical abundances in the dense interiors of molecular clo uds, increasing the abundances for C and C+ and most carbon-bearing sp ecies and lowering the abundances for some other species such as H2O a nd O-2. These results, which can be explained in the context of the ex isting ion-neutral reaction scheme in terms of electron abundance chan ges due to diffusion, appear to agree with observations.