Thermal desorption of C₆ H₆ from surfaces of astrophysical relevance

The thermal desorption of C₆ H₆ from two astrophysically relevant surfaces has been studied using temperature programmed desorption. Desorption from an amorphous SiO₂ substrate was used as a mimic for bare interstellar grains, while multilayer films of amorphous solid water (ASW) were used to study the adsorption of C₆ H₆ on grains surrounded by H₂ O dominated icy mantles. Kinetic parameters were obtained through a combination of kinetic modeling, leading edge analysis, and by considering a distribution of binding sites on the substrate. The latter is shown to have a significant impact on the desorption of small exposures of C₆ H₆ from the amorphous SiO₂ substrate. In the case of adsorption on ASW, dewetting behavior and fractional order desorption at low coverage strongly suggest the formation of islands of C₆ H₆ on the H₂ O surface. The astrophysical implications of these observations are briefly outlined. © 2009 American Institute of Physics.