Chemical effects of irregular interstellar oxide grains

The importance of chemically-active geometrical surface sites on the surfaces of interstellar oxide grains is discussed in terms of their catalytic behaviour in molecular formation. Surface features — such as steps and corners — are considered in detail, and the binding energies of the hydrogen atom and the proton at these sites are estimated. It appears likely that chemical effects of interstellar oxide grains are located not only at point defects discussed elsewhere, but also at these geometrical surface features. Adsorbed surface species, surface reaction schemes, and the possible effects of grain impurities are briefly considered.