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Paper: Ionization and Desorption of Molecule Ice Stimulated by X-Rays in Circumstellar Envelopes
Volume: 464, Circumstellar Dynamics at High Resolution
Page: 361
Authors: Mendoza, E. F.; Almeida, G.; Wolff, W.; Andrade, D. P. P.; Rocco, M. L. M.; Boechat-Roberty, H. M.
Abstract: The HCN and C2H2 molecules present in protoplanetary disks can form the Nitrogen-containing cyclic organic molecules (N-heterocycles) that play important roles in terrestrial biology, for example as the nucleobases in genetic material. In this work the ionization, dissociation and desorption processes of pyrimidine ice, a nucleotide precursor molecule, were experimentally studied applying the time-of-flight mass spectrometry technique, in order to evaluate their destruction pathways in protoplanetary disks. These processes were stimulated by soft X-rays from 397 to 430 eV delivered by synchrotron light source. The photodesorption ion yield (ion photon-1) of several ions such as HCN+, C4H2+, HC3NH+, and C3H3N+ among other ionic fragments were determined. Considering that TW Hydrae has an integrated X-ray luminosity (LX) from 0.2 to 2 keV of ∼ 1 × 1030 erg s-1, the ion flux (ion cm–2 s-1) desorbed from the grain surface and the ion production rate (ion cm–3 s-1) were determined as a function of the distance from the central star. The results show that ionic species are formed from ice due to photons interaction, highlighting the role of the ice chemistry in the molecular enrichment in protoplanetary disks.
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