Electron attachment to interstellar grains

Abstract

We have computed the cross-section for electron collisions with spherical grains at low energies, using both classical and quantum (wave) mechanics. The calculations were found to agree for grain radii as small as 3 × 10 -6 cm and collision energies E/k = 10 K. On the other hand, the results of the classical calculations for smaller grains exceed those of wave mechanics by typically a factor of 2, owing to interference effects, which are not present in the classical limit. We suggest that the greatest uncertainty in electron attachment rates is in the value of the sticking coefficient, which may be expected to vary considerably with the composition of the grain and its mantle.