標題: Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
作者: Cheng, Bing-Ming
Lu, Hsiao-Chi
Chen, Hong-Kai
Bahou, Mohammed
Lee, Yuan-Pern
Mebel, Alexander M.
Lee, L. C.
Liang, Mao-Chang
Yung, Yuk L.
應用化學系
應用化學系分子科學碩博班
Department of Applied Chemistry
Institute of Molecular science
關鍵字: astrochemistry;methods : laboratory;molecular data
公開日期: 20-Aug-2006
摘要: Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 in the spectral region 140-220 nm were determined at similar to 298 K using synchrotron radiation. Absorption spectra of NH2D and NHD2 were deduced from spectra of mixtures of NH3 and ND3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH2D, NHD2, and ND3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A X and B X systems of NH3 agree satisfactorily with previous reports; values for NH2D, NHD2, and ND3 agree with quantum chemical predictions. The photolysis of NH3 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 NH3 and NH2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH2D is lower than that of NH3 by as much as 30%. The D/H ratio in NH2D/NH3 for tracing the microphysics in the troposphere of Jupiter is also discussed.
URI: http://dx.doi.org/10.1086/505615
http://hdl.handle.net/11536/11909
ISSN: 0004-637X
DOI: 10.1086/505615
期刊: ASTROPHYSICAL JOURNAL
Volume: 647
Issue: 2
起始頁: 1535
結束頁: 1542
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