UV photodestruction of CH bonds and the evolution of the 3.4 μ m feature carrier

Abstract

Experiments simulating the processing of various hydrocarbon speciesunder diffuse and dense cloud conditions by UV irradiation were performed.The results indicate that such molecules will be efficiently dehydrogenatedin interstellar space. It is argued that the presence of hydrogenin the aliphatic grain material in diffuse clouds results from anequilibrium between dehydrogenation by UV processing and re-hydrogenationby the impinging atomic gas. In dense clouds, the presence of theice layer will prevent the re-hydrogenation process, causing thecarbonaceous grain material to be gradually de-hydrogenated if UVphotons are able to penetrate into the dense medium. The implicationsof this study for the evolution of the carbonaceous component ofdust in the interstellar medium are discussed.