Chemistry in Turbulent Flows

Summary

The ubiquitous amount of interstellar CH⁺ in translucent molecular clouds presents one of the outstanding problems of interstellar chemistry. The chemical pathways which lead to the formation and the destruction of the CH⁺ ion in the quiescent gas are well understood, yet the predicted abundances are orders of magnitudes below the observed values. This led to the suggestion that disturbances upon the quiescent material increase the CH⁺ formation rate via the reaction C⁺ + H₂ → CH⁺ + H, which is endothermic by 4650 K. Interstellar turbulence may very well provide the energy source to drive this reaction. The various formation scenarios of interstellar CH⁺ are discussed, with an emphasis on processes which involve the dissipation of interstellar turbulence. The chemical properties of regions which are affected by the dissipation of turbulence are summarized.

Introduction

Interstellar turbulence may affect the chemistry of translucent and dense molecular clouds in various ways. Turbulent mixing of material from dense cores to the surface of molecular clouds, and vice versa, may alter the abundances inferred from chemical networks. In particular, turbulent transport and diffusion was invoked to explain the large abundance of atomic carbon and that of complex organic molecules which is observed in dense molecular clouds (Boland & de Jong 1982; Chièze, Pineau des Forêts & Herbst 1991; Xie, Allen & Langer 1995).

The dissipation of turbulence in translucent molecular clouds is another physical process which has recently been considered to alter chemical abundances.