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

Turbulence in molecular clouds is well recognized, but the resultant diffusive transport and its effects on the chemical structure of the clouds have not been extensively investigated. We present in this article a study using the mixing-length approximation of the effects of turbulent diffusion on the chemical structure of a representative dark molecular cloud. With a diffusion term in the continuity equation for each species, we model the time-dependent gas-phase chemistry in a dense molecular cloud with fixed density and temperature profiles. We estimate the diffusion coefficient based on the observed turbulence in molecular clouds and find that diffusive processes significantly modify the predicted chemical abundances in the dense interiors of molecular clouds, increasing the abundances for C and C+ and most carbon-bearing species and lowering the abundances for some other species such as H2O and O-2. These results, which can be explained in the context of the existing ion-neutral reaction scheme in terms of electron abundance changes due to diffusion, appear to agree with observations.