2015A&A...581A..92J

The photolysis of hydrogenated amorphous carbon, a-C(:H), dust by UV photon-irradiation in the laboratory leads to the release of H₂ as well as other molecules and radicals. This same process is also likely to be important in the interstellar medium. We investigate molecule formation arising from the photo-dissociatively-driven, regenerative processing of a-C(:H) dust. We explore the mechanism of a-C(:H) grain photolysis leading to the formation of H₂ and other molecules/radicals. The rate constant for the photon-driven formation of H₂ from a-C(:H) grains is estimated to be 2x10^–17cm³/s. In intense radiation fields photon-driven grain decomposition will lead to fragmentation into daughter species rather than H₂ formation. The cyclic re-structuring of arophatic a-C(:H) nano-particles appears to be a viable route to formation of H₂ for low to moderate radiation field intensities (1≲G₀≲10²), even when the dust is warm (T∼50-100K).