Efficiency of the top-down polycyclic aromatic hydrocarbon-to-fullerene conversion in ultraviolet irradiated environments

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) and fullerenes play a major role in the physics chemistry of interstellar medium (ISM). Based on number recent experimental theoretical investigations we developed model which PAHs are subject to photo-dissociation (carbon hydrogen loss) hydrogenation. We take into account that dehydrogenated may fold closed structures – fullerenes. Fullerenes, their turn, can be also hydrogenated, becoming fulleranes, photo-dissociated, losing carbon atoms. The loss leads shrinking fullerene cages smaller ones. calculate abundance different sizes hydrogenation level depending external conditions: gas temperature, intensity radiation field, density atoms, electrons. highlight conditions, favourable for formation from PAHs, conclude this mechanism works not only H-poor environment but at modest values up 104 cm−3. found fulleranes formed ISM, although fraction atoms locked them maximum around 10−9. applied our two regions, Orion Bar NGC 7023. compare estimates synthetic band intensities these objects with observations gives good results closest surroundings ionizing stars. demonstrate additional channels should operate along ultraviolet (UV)-induced explain far UV sources.