Behaviour of radicals on interstellar dust analogues

Abstract

Surface reactions of radicals play important roles in the formation of complex molecules on interstellar dust grains. Under interstellar conditions, because the coverage of adsorbates on dust is significantly low, surface reactions are often limited by precedent processes, namely, the adsorption and diffusion of reactants. Therefore, to appropriately incorporate dust surface reactions into chemical models, information on the adsorption and diffusion of radicals is crucial. However, it is not easy to follow the behaviour of radicals on surfaces by conventional experimental methods. To monitor radicals on interstellar dust analogues, we have recently succeeded in applying a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods. In this paper, we briefly review our recent experiments for clarifying radical behaviour on water ice, pure solid CO and diamond-like carbon.

Vacuum Ultraviolet Photolysis of Condensed Methyl Chloride in Interstellar Model Conditions and Trapping of Intermediates at Intergrain Interfaces

“…The higher methane and dichloromethane production in crystalline than polycrystalline materials could be because radical migration is feasible in periodic crystalline materials. However, polycrystalline solids are composed of crystal domains with existing crystalline grain boundaries, and these grain-bound molecules play a vital role in the process of photolysis . The presence of a thermal energy barrier on these boundaries is crucial, as it hinders radicals from moving between different crystalline grains.…”