Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
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DOI：
10.1086/505615
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发表时间：
2006-08-20
影响因子：
4.9
通讯作者：
Yung, Yuk L.
中科院分区：
文献类型：
--
作者：
Cheng, Bing-Ming;Lu, Hsiao-Chi;Yung, Yuk L.
在298 K附近用同步辐射测定了NH_3、NH_2D、NHD_2和ND_3在140-220 nm光谱区的光吸收截面。NH_2D和NHD_2的吸收光谱是由NH_3和ND_3的混合物的吸收光谱推导出来的，其中四种同位素体的平衡浓度都服从统计分布。NH 2D、NHD 2和ND 3的横截面是新的。振荡器的强度，吸收截面的光谱线的集成，为A X和B X系统的NH3同意令人满意地与以前的报告，NH 2D，NHD 2，和ND 3同意与量子化学预测值。NH3的光分解提供了木星等巨行星的平流层下部和对流层上部的活性氢的主要来源。将NH_3和NH_2D的光吸收截面代入木星大气的Caltech/JPL光化学扩散模型，发现NH_2D的光解效率比NH_3低30%。本文还讨论了NH_2D/NH_3中的D/H比对木星对流层微物理的示踪作用。
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.