Electron transfer in ion-dust grain collisions

The rate coefficient β is determined for the transfer of electrons from negatively-charged dust grains to positive ions (charge Zsub(i)e) during collisions and close encounters in a gas of temperature T. Complete neutralization of the ions is the most likely result, with β approximately equal to the grain geometrical cross-section times the mean ion speed times a Coulomb factor (1 + 2.5 Zsub(i)). For a normal interstellar dust to gas mass ratio (approximately 10-2), this neutralization process is slower than radiative recombination by a factor of about (Zsub(i) x 107K/T). However, even at T = 104K, charge transfer with grains can significantly increase the concentrations of neutral atoms of elements that predominantly are at least twice ionized. (author)