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 Title: Isotope Selective Photodissociation Of By The Interstellar Radiation Field And Cosmic Rays Author(s): Heays, Alan Contributor(s): Gibson, Stephen; Lewis, Brenton R.; Ubachs, Wim; Gredel, Roland; Visser, Ruud; van Dishoeck, Ewine Subject(s): Mini-symposium: Astronomical Molecular Spectroscopy in the Age of ALMA Abstract: Photodissociation of $^{14}$N$_2$ and $^{14}$N$^{15}$N occurs in interstellar clouds, protoplanetary discs, (exo)planetary atmospheres, and other environments due to ultraviolet radiation originating from stellar sources and the presence of cosmic rays. We study this process in detail in search of an explanation for the observed non-elemental ratios of N isotopologues observed in solar system bodies and in molecular clouds. High-resolution theoretical photodissociation cross sections of N$_2$ and competing UV-absorbing species are used to calculate the isotope-selective shielding of N$_2$ in photochemical models of a diffuse interstellar cloud and protoplanetary disk. An enhancement of the atomic $^{15}$N/$^{14}$N ratio over the elemental value is obtained due to the self-shielding of external radiation at an extinction of about $A_v=1$\,mag, and leads to a similar mass fractionation in daughter species. This effect is larger where assumed grain growth has reduced the opacity of dust to ultraviolet radiation. The cosmic-ray induced dissociation of N$_2$ is calculated from a high-resolution model of H$_2$ emission and is found to depend sensitively on details of the emission and photodissociation cross sections. Issue Date: 2014-06-19 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Heays, A.; Gibson, S.; Lewis, B.R.; Ubachs, W.; Gredel, R.; Visser, R.; van Dishoeck, E. ISOTOPE SELECTIVE PHOTODISSOCIATION OF BY THE INTERSTELLAR RADIATION FIELD AND COSMIC RAYS. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.RA10 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/51042 DOI: https://doi.org/10.15278/isms.2014.RA10 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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