SIMBAD references

Laboratory experiments show that the thermal heterogeneous reactions of oxygen atoms may contribute to the synthesis of epoxides in interstellar clouds. The data set also indicates that the contribution of these pathways to epoxide formation, in comparison to non-thermal routes, is likely to be strongly temperature dependent. Our results indicate that an increased abundance of epoxides, relative to the corresponding aldehydes, could be an observational signature of a significant contribution to molecular oxidation via thermal O atom reactions with alkenes. Specifically surface science experiments show that both C₂H₄ O and C₃H₆O are readily formed from reactions of ethene and propene molecules with thermalized oxygen atoms at temperatures in the range of 12-90 K. It is clear from our experiments that these reactions, on a graphite surface, proceed with significantly reduced reaction barriers compared with those operating in the gas phase. For both the C₂H₄+ O and the C₃H₆+ O reactions, the surface reaction barriers we determine are reduced by approximately an order of magnitude compared with the barriers in the gas phase. The modeling of our experimental results, which determines these reaction barriers, also extracts desorption energies and rate coefficients for the title reactions. Our results clearly show that the major product from the O + C₂H₄ reaction is ethylene oxide, an epoxide.