Impact of oxygen chemistry on model interstellar grain surfaces

Temperature-programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS) are used to probe the effect of atomic and molecular oxygen (O and O 2 ) beams on amorphous silica (aSiO 2 ) and water (H 2 O) surfaces (porous-amorphous solid water; p-ASW, compact amorphous solid water; c-ASW, and crystalline solid water; CSW). Altering the deposition method of O 2 is shown to result in different desorption energies of O 2 due to differences in O 2 film morphology when deposited on the aSiO 2 surface. O 2 enthalpy of formation is dissipated into the aSiO 2 substrate without changes in the silica network. However, on the H 2 O surfaces, O 2 formation enthalpy release is dissipated into the H-bonded matrix leading to morphological changes, possibly compacting p-ASW into c-ASW while CSW appears to undergo amorphisation. The enthalpy release from O 2 formation is, however, not enough to result in reactive desorption of O 2 or H 2 O under the current experimental circumstances. Further to this, O 2 formation on sub-monolayer quantities of H 2 O leads to enhanced de-wetting and a greater degree of H-bond reconnection in H 2 O agglomerates. Lastly, O 3 is observed from the O + O 2 reaction on all surfaces studied. Temperature-programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS) are used to probe the effect of atomic and molecular oxygen (O and O 2 ) beams on amorphous silica (aSiO 2 ) and water (H 2 O) surfaces (porous-amorphous solid water; p-ASW, compact amorphous solid water; c-ASW, and crystalline solid water; CSW).