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Title: Branching Ratios in Vacuum Ultraviolet Photodissociation of CO and N 2: Implications for Oxygen and Nitrogen Isotopic Compositions of the Solar Nebula

Abstract

NASA's Genesis mission reveals that the rare isotope 15N is approximately seven times more enriched than the rare isotopes 17O and 18O in the terrestrial planets relative to the Sun. Here, we explain this peculiar observation under the framework of self-shielding and the difference in chemical reactivity between the excited O( 1 D) [N( 2 D)] and the ground O( 3 P) [N( 4 S)] states produced by VUV photodissociation of CO [N 2]. After weighting the absorption cross-sections for individual photodissociation bands, and taking into account the mutual shielding by H 2, the CO/N 2 ratio, and the partition of O and N among gas:ice:dust phases in the solar nebula, we show that the trapping of N( 2 D) via hydrogenation is favored over that of O( 1 D). As a result, this provides a possible explanation of the Genesis results and supports the self-shielding model as the primary mechanism for generating isotopic anomalies of O and N in the early solar nebula.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3];  [2];  [2]; ORCiD logo [4]; ORCiD logo [2]
  1. Univ. of California, Davis, CA (United States); Univ. of California, San Francisco, CA (United States)
  2. Univ. of California, Davis, CA (United States)
  3. Univ. of California, Davis, CA (United States); Univ. of Basel, Basel (Switzerland)
  4. Univ. of California, San Francisco, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1508556
Report Number(s):
LA-UR-18-28857
Journal ID: ISSN 1538-4357
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 850; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; Planetary Sciences; astrochemistry; ISM: molecules; meteors; meteoroids; protoplanetary disks; solar wind; Sun: abundances

Citation Formats

Shi, Xiaoyu, Yin, Qing -Zhu, Gao, Hong, Chang, Yih -Chung, Jackson, William M., Wiens, Roger Craig, and Ng, Cheuk -Yiu. Branching Ratios in Vacuum Ultraviolet Photodissociation of CO and N2: Implications for Oxygen and Nitrogen Isotopic Compositions of the Solar Nebula. United States: N. p., 2017. Web. doi:10.3847/1538-4357/aa8ee7.
Shi, Xiaoyu, Yin, Qing -Zhu, Gao, Hong, Chang, Yih -Chung, Jackson, William M., Wiens, Roger Craig, & Ng, Cheuk -Yiu. Branching Ratios in Vacuum Ultraviolet Photodissociation of CO and N2: Implications for Oxygen and Nitrogen Isotopic Compositions of the Solar Nebula. United States. doi:10.3847/1538-4357/aa8ee7.
Shi, Xiaoyu, Yin, Qing -Zhu, Gao, Hong, Chang, Yih -Chung, Jackson, William M., Wiens, Roger Craig, and Ng, Cheuk -Yiu. Wed . "Branching Ratios in Vacuum Ultraviolet Photodissociation of CO and N2: Implications for Oxygen and Nitrogen Isotopic Compositions of the Solar Nebula". United States. doi:10.3847/1538-4357/aa8ee7. https://www.osti.gov/servlets/purl/1508556.
@article{osti_1508556,
title = {Branching Ratios in Vacuum Ultraviolet Photodissociation of CO and N2: Implications for Oxygen and Nitrogen Isotopic Compositions of the Solar Nebula},
author = {Shi, Xiaoyu and Yin, Qing -Zhu and Gao, Hong and Chang, Yih -Chung and Jackson, William M. and Wiens, Roger Craig and Ng, Cheuk -Yiu},
abstractNote = {NASA's Genesis mission reveals that the rare isotope 15N is approximately seven times more enriched than the rare isotopes 17O and 18O in the terrestrial planets relative to the Sun. Here, we explain this peculiar observation under the framework of self-shielding and the difference in chemical reactivity between the excited O(1D) [N(2D)] and the ground O(3P) [N(4S)] states produced by VUV photodissociation of CO [N2]. After weighting the absorption cross-sections for individual photodissociation bands, and taking into account the mutual shielding by H2, the CO/N2 ratio, and the partition of O and N among gas:ice:dust phases in the solar nebula, we show that the trapping of N(2D) via hydrogenation is favored over that of O(1D). As a result, this provides a possible explanation of the Genesis results and supports the self-shielding model as the primary mechanism for generating isotopic anomalies of O and N in the early solar nebula.},
doi = {10.3847/1538-4357/aa8ee7},
journal = {The Astrophysical Journal (Online)},
issn = {1538-4357},
number = 1,
volume = 850,
place = {United States},
year = {2017},
month = {11}
}

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