Non-thermal Chemistry in the Interstellar Medium

Abstract

The evidence for turbulence in interstellar molecular clouds, and the possible sources of the turbulence in the interstellar medium, are described. The chemical consequences of the dissipation of turbulent energy are considered. A model is developed in which the ambient cold cloud includes a number of short-lived turbulent dissipative (warm) regions and some longer lived relaxation phases. Such a model is shown to be capable of accounting for the essential chemistry in diffuse molecular clouds. Studies of chemistry in magnetized shocks are also discussed, and applications to the chemistry of interstellar sulfur are described. The effects of magnetized turbulence on dust grains are considered and it is shown that dust grains may in some circumstances grow by accretion, while in others the grains may be eroded by collisions with gaseous molecules or in grain–grain collisions. The formation of (detected) small-scale transient structures in the interstellar medium is explored and the chemistry within them is evaluated.