Formation of molecular oxygen and ozone on amorphous silicates

Oxygen in the interstellar medium is seen in the gas phase, in ices (incorporated in H₂O, CO, and CO₂), and in grains such as (Mg _x Fe_{1- x} )SiO₃ or (Mg _x Fe_{1- x} )₂SiO₄, 0 < x < 1. In this investigation, we study the diffusion of oxygen atoms and the formation of oxygen molecules and ozone on the surface of an amorphous silicate film. We find that ozone is formed at low temperature (<30K), and molecular oxygen forms when the diffusion of oxygen atoms becomes significant, at around 60K. This experiment, besides being the first determination of the diffusion energy barrier (1785 ± 35 K) for oxygen atoms on a silicate surface, suggests bare silicates as a possible storage place for oxygen atoms in low-A_v environments.