2008ApJ...682L.101M

We present the first results of laboratory research on the processing of nano-sized carbon particles under simulated dense-medium conditions. The experiments aim to study the variations of the degree of hydrogenation of carbon particles covered with a water ice layer in response to H atom exposure. The effects of H atom processing have been studied by means of IR spectroscopy. The results show that the formation of C-H bonds in the aliphatic CH₂and CH₃ functional groups does not take place. The activation of a band at 3.47 µm is observed. It is assigned to the C-H stretching vibration of tertiary sp³ carbon atoms. The band profile is compatible with that present in the spectrum of sources embedded in dense clouds. We propose that the carbon grain population, which is responsible for the interstellar aliphatic 3.4 µm band in diffuse regions, absorbs at 3.47 µm in dense clouds.