Activation of the 3.4 Micron Band in Carbon Grains by Exposure to Atomic Hydrogen

Abstract

We present the results of an experiment aimed at studying the interaction of atomic hydrogen with nano-sized carbon grains. The effects induced by H processing have been studied by infrared spectroscopy. C–H stretching and bending modes are activated after H atom exposure. In particular, the 3.4 μm feature fits quite well to the absorption band observed in the diffuse interstellar medium toward the Galactic center as well as in the proto-planetary nebula CRL 618. The estimated efficiency of the process is such that one C–H bond is formed per 16 hydrogen atoms impinging on the sample. The results we obtained have important implications for the formation and evolution of carbon materials responsible for the 3.4 μm absorption band both in the diffuse interstellar medium and in the circumstellar outflows during the transition from the asymptotic giant branch to planetary nebula phases.