Charge Variation of Polycyclic Aromatic Hydrocarbons in the Diffuse Interstellar Medium

Abstract

We have modelled the charge balance for several polycyclic aromatic hydrocarbon (PAH) molecules, the fullerene C60 and small graphitic grains in the diffuse interstellar medium (ISM). For the smaller PAH molecules, we used pyrene (C16H10), pentacene (C22H14) and coronene (C24H12). We then calculated the charge distribution for each particle as a function of electron density, radiation field ana depth at which it was situated in a diffuse cloud. For typical conditions in the diffuse ISM, the charge distribution is determined to a large extent by PAH electron affinity, which determines whether an electron will stick to it. For the PAH molecules, we compare the charge distribution calculated using experimentally measured cation-electron recombination rates with theoretically determined rates. We conclude that while a PAH mixture may exist in a variety of singley charged and neutral states, larger disk shaped and spherical grains will be predominantly neutral.KeywordsPolycyclic Aromatic HydrocarbonElectron AffinityIonization Cross SectionCharge VariationDiffuse CloudThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.