Molecular cloud abundances and anomalous diffusion

The chemistry of molecular clouds has been studied for decades, with an increasingly general and sophisticated treatment of the reactions involved. Yet the treatment of turbulent di ffusion has remained extremely sketchy, assuming simple Fickian diffusion with a scalar diffusivity D. However, turbulent flows similar to those in the interstell ar medium are known to give rise to anomalous diffusion phenomena, more specifical ly superdiffusion (increase of the diffusivity with the spa tial scales involved). This paper considers to what extent and in what sense superdiffusion modifies molecular abundances in interstellar clouds. For this first exploration of the sub ject we employ a very rough treatment of the chemistry and the effect of non-unifom cloud density on the diffusion equation is also treated in a simplified way. The results nevertheles s clearly demonstrate that the effect of superdiffusion is qu ite significant, abundance values at a given radius being mod ified by order of unity factors. The sense and character of this infl uence is highly nontrivial.