Electron attachment rates for PAH anions in the ISM and dark molecular clouds: dependence on their chemical properties

Abstract

Context. The attachment of free electrons to polycondensed aromatic ring molecules (PAHs) is studied for the variety of these molecules with different numbers of condensed rings and over a broad range of electron temperatures, using a multichannel quantum scattering approach. The calculations of the relevant cross sections are used in turn to model the corresponding attachment rates for each of the systems under study, and these rates are parametrized as a function of temperature using a commonly employed expression for two-body processes in the interstellar medium (ISM). Aims. The scope of this work is to use first principles to establish the influence of chemical properties on the efficiency of the electronattachment process for PAHs. Methods. Quantum multichannel scattering methods are employed to generate the relevant cross sections, hence the attachment rates, using integral elastic cross sections computed over a broad range of relevant energies, from threshold up to 1000 K and linking the attachment to low-energy resonant collisions. Results. The rates obtained for the present molecules are found to markedly vary within the test ensemble of the present work and to be lower than the earlier values used for the entire class of PAHs anions, when modelling their evolutions in ISM environments. The effects of such differences on the evolutions of chemical networks that include both PAH and PAH-species are analysed in some detail and related to previous calculations.

Negative Ions in Space

“…Carelli et al applied their molecular-scale calculations of electron attachment to molecules and used them to predict radiative electron attachment rates at different temperatures for polyaromatic hydrocarbons (PAHs) and linear carbon-chain molecules . They used these predicted rates to model anion abundances in the ISM.…”

Anisotropy and Size Effects on the Optical Spectra of Polycyclic Aromatic Hydrocarbons

“…Polycyclic aromatic hydrocarbons (PAHs) are the focus of research in significantly diverse fields, ranging from biochemistry 1 to theoretical chemistry, 2 from molecular electronics 3 to astrochemistry, 4 where PAHs are assigned an important role 5,6 due to their chemical composition and spectral features. [7][8][9][10][11] In this framework, a theoretical identification of the absorption and emission features of these molecules assumes a significant relevance, 12,13 since they might drastically vary both upon small structural modifications 14,15 and as a consequence of ionization [16][17][18][19] or dehydrogenation. [20][21][22][23] In the field of molecular electronics, the interest in medium-and large-sized PAHs is intrinsically connected to graphene, as they are viewed as highly stable graphene molecules.…”

Structure and dynamics of near-threshold leptons driven by dipolar interactions: an accurate computational study for the DNA purinic bases

“…In the parallel language of the radiative stabilization mechanisms under the conditions of the Interstellar Medium [54,55], one can then say that the overlap integrals between DSS and DBS configurations of a given molecular environment are now expected to be very large and therefore favour radiative transitions between such states. In the more dense conditions of a biological environment this concept translates into the suggestion that the small energy gaps between DSS and DBS anions could favour the formation of the DBS structures of the NB molecules.…”