The influence of grains on the propagation and structure of C-type shock waves in interstellar molecular clouds

Gas-grain interactions can have important consequences for the physics and chemistry of shock waves propagating in molecular clouds. The grains can be both a source and a sink of molecules, and their inertia can modify the dynamics of the propagation of, in particular, C-type shock waves. The degree of charging of the grains, both in the pre-shock gas and in the shock wave itself, is a significant parameter. The population of interstellar grains extends from large molecules, which we represent by polycyclic aromatic hydrocarbons, to much larger particles, composed of silicates and amorphous carbon material. The influence of the inertia of the grains on the dynamics of the flow is modelled in detail, and upper limits to the velocities of C-type shock waves are established. We find that collisions between charged and neutral grains, driven by ion-neutral drift in C-type shock waves, may lead to the shattering of a large fraction of the amorphous carbon material.