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Absorption Cross Sections of NH_3, NH_2D, NHD_2, and ND_3 in the Spectral Range 140-220 nm and Implications for Planetary Isotopic Fractionation

Cheng, Bing-Meng and Lu, Hsiao-Chi and Chen, Hong-Kai and Bahou, Mohammed and Lee, Yuan-Pern and Mebel, Alexander M. and Lee, L. C. and Liang, Mao-Chang and Yung, Yuk L. (2006) Absorption Cross Sections of NH_3, NH_2D, NHD_2, and ND_3 in the Spectral Range 140-220 nm and Implications for Planetary Isotopic Fractionation. Astrophysical Journal, 647 (2). pp. 1535-1542. ISSN 0004-637X. doi:10.1086/505615.

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Cross sections for photoabsorption of NH_3, NH_2D, NHD_2, and ND_3 in the spectral region 140-220 nm were determined at ~298 K using synchrotron radiation. Absorption spectra of NH_2D and NHD_2 were deduced from spectra of mixtures of NH_3 and ND_3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH_2D, NHD_2, and ND_3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A ← X and B ← X systems of NH_3 agree satisfactorily with previous reports; values for NH_2D, NHD_2, and ND_3 agree with quantum chemical predictions. The photolysis of NH_3 provides a major source of reactive hydrogen in the lower stratosphere and upper troposphere of giant planets such as Jupiter. Incorporating the measured photoabsorption cross sections of NH_3 and NH_2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH_2D is lower than that of NH_3 by as much as 30%. The D/H ratio in NH_2D/NH_3 for tracing the microphysics in the troposphere of Jupiter is also discussed.

Item Type:Article
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URLURL TypeDescription
Liang, Mao-Chang0000-0002-5294-9344
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 2006 American Astronomical Society. Received 2006 February 9; accepted 2006 May 2. B.-M. C. and Y.-P. L. thank the National Science Council of Taiwan (grants NSC93-2113-M-213-002 and NSC93-2113- M-009-019) for support. L. C. L. thanks for the National Synchrotron Radiation Research Center in Taiwan for a visiting professorship. M.-C. L. and Y. L. Y. were supported by NASA grant NASA5-13296 to the California Institute of Technology.
Funding AgencyGrant Number
National Science Council of TaiwanNSC93-2113-M-213-002
National Science Council of TaiwanNSC93-2113- M-009-019
National Synchrotron Radiation Research Center in TaiwanUNSPECIFIED
Subject Keywords:astrochemistry; methods: laboratory; molecular data
Issue or Number:2
Record Number:CaltechAUTHORS:20110218-095953129
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Official Citation:Bing-Ming Cheng et al. 2006 ApJ 647 1535 doi: 10.1086/505615
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22380
Deposited On:18 Feb 2011 19:44
Last Modified:09 Nov 2021 16:04

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