Isotope selective photodissociation of N-2 by the interstellar radiation field and cosmic rays

摘要: Context. Photodissociation of N2 and 14N15N occurs in interstellar clouds, circumstellar envelopes, protoplanetary discs, other environments due to ultraviolet radiation originating from stellar sources the presence cosmic rays. This source N atoms initiates formation more complex N-bearing species may influence their isotopic composition. Aims. We study photodissociation rates by continuum both isotopologues a field ray induced photons. To determine effect these on composition molecules. Methods. High-resolution theoretical cross sections are used an accurate comprehensive quantummechanical model molecule based laboratory experiments. A similarly high-resolution spectrum H2 emission following interactions with rays has been constructed. The spectroscopic data calculate which then input into isotopically differentiated chemical models, describing cloud disc. Results. rate Draine assuming 30 K excitation is 1.73 × 10−10 s−1, within 4% for N2, photons ionisation ζ = 10 −16 s−1 about 10−15 up factor difference between isotopologues. Shielding functions H2, H presented. Incorporating model, enhancement atomic 15N/14N ratio over elemental value obtained self-shielding external at extinction 1.5 mag. larger where assumed grain growth reduced opacity dust radiation. transfer photolytic fractionation molecules demonstrated be significant disc growth, dependent 15N approaching HCN. dissociation CO revisited employing recent section, leading that ∼40% lower than previously calculated.