2015ApJ...804...24S

The vacuum ultraviolet (VUV) synthesis of CO and CO₂ on ice-coated graphite and isotopic labeled ¹³C graphite has been examined for temperatures between 40 and 120 K. The results show that CO and CO₂can be formed at the buried ice:graphite interface with Lyα photon irradiation via the reaction of radicals (O and OH) produced by direct photodissociation and the dissociative electron attachment of the interfacial water molecules. The synthesized CO and CO₂molecules can desorb in hot photon-dominated regions and are lost to space when ice coated carbonaceous dust grains cycle within the protoplanetary disks. Thus, the nonthermal formation of CO and CO₂at the buried ice:grain interface by VUV photons may help regulate the carbon inventory during the early stage of planet formation. This may contribute to the carbon deficits in our solar system and suggests that a universal carbon deficit gradient may be expected within astrophysical bodies surrounding center stars.