GRAIN-MANTLE EROSION IN MAGNETOHYDRODYNAMIC SHOCKS

Models of C-type shocks have been computed that include, for the first time, the dynamical and chemical effects of PAH molecules and the chemical and thermal effects of adsorption to and desorption from grains. We find that the sputtering associated with the relative motion of the ions and the neutrals within the shock can completely remove the grain mantles for shock velocities as low as 10 km s-1. Readsorption occurs when the ion-neutral velocity difference becomes insufficient to overcome the binding energy of the molecules to the mantles. We find that the column densities of molecules such as NH3 can be greatly enhanced by sputtering, assuming that saturated species are produced in the mantles.