Radial distribution of production rates, loss rates and densities corresponding to ion masses ≤ 40 amu in the inner coma of Comet Halley : Composition and chemistry
Radial distribution of production rates, loss rates and densities corresponding to ion masses ≤ 40 amu in the inner coma of Comet Halley : Composition and chemistry
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哈雷彗星内彗发中离子质量≤ 40 amu 对应的生成率、损失率和密度的径向分布：成分和化学
DOI：
10.1016/j.icarus.2005.02.019
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发表时间：
2005
期刊：
影响因子：
3.2
通讯作者：
A. Bhardwaj
中科院分区：
文献类型：
--
作者：
S. Haider;A. Bhardwaj
本文研究了1 P/Halley彗星内彗发中质量为140 amu的离子所对应的C、H、N、O和S化合物的化学。的生产率，损失率，和离子质量密度的计算使用的分析产率谱方法和求解耦合连续性方程控制的稳态光化学平衡条件。模型中的主要电离源是太阳极紫外光子、光电子和太阳风起源的极光电子。该化学模型通过600多个化学反应耦合了离子、中性粒子、电子和光子之间的离子中性、电子中性、光子中性和电子-离子反应。在模型中考虑的46种离子中，24种重要离子的化学性质（即，CH_3OH ~+2、H_3CO ~+、NH ~+4、H_3S ~+、H_2CN ~+、H_2O ~+、NH ~+3、CO ~+、C_3H ~+3、OH ~+、H_3O ~+、CH_3OH ~+、C_3H ~+4、C_2H ~+2、C_2H ~+、HCO ~+、S ~+、CH ~+3、H_2S ~+、O ~+、C ~+、CH ~+4、C ~+2、O ~+2）。在径向距离<1000 km处，电子密度主要由6个离子控制，即，NH+4、H3 O+、CH 3OH +2、H3 S+、H2 CN+和H2O+，按其相对贡献的降序排列。然而，在距离>1000 km时，6种主要离子是H3 O+、CH 3OH +2、H2O+、H3CO+、C2 H +2和NH+4;沿着离子CO+、OH+和HCO+，其重要性随着径向距离的进一步增加而增加。研究发现，在径向距离大于1000 km（±500 km）时，支配内彗发中几种重要离子的产生和损失的主要化学过程与在径向距离小于1000 km时的主要化学过程不同。本研究清楚地揭示了光电子碰撞电离的重要性，以及太阳EUV、极光和光电子电离源在内彗发中的相对贡献。计算出的离子质量密度进行了比较与乔托离子质谱仪（IMS）和中性质谱仪（NMS）的数据在径向距离1500，3500和6000公里。模型计算和Giotto测量之间存在合理的一致性。在IMS光谱中的9个主峰之间的质量10和40 amu的复制相当不错的模型内的电离层顶内的一个因素。我们已经提出了简单的公式来计算九个主要离子的密度，这有助于在IMS光谱中的九个主峰，在整个内彗发，这将是有用的，在估计它们的密度，而无需运行复杂的化学模型。
In this paper we have studied the chemistry of C, H, N, O, and S compounds corresponding to ions of masses ⩽40 amu in the inner coma of the Comet 1P/Halley. The production rates, loss rates, and ion mass densities are calculated using the Analytical Yield Spectrum approach and solving coupled continuity equation controlled by the steady state photochemical equilibrium condition. The primary ionization sources in the model are solar EUV photons, photoelectrons, and auroral electrons of the solar wind origin. The chemical model couples ion–neutral, electron–neutral, photon–neutral and electron–ion reactions among ions, neutrals, electrons, and photons through over 600 chemical reactions. Of the 46 ions considered in the model the chemistry of 24 important ions (viz., CH3OH+2, H3CO+, NH+4, H3S+, H2CN+, H2O+, NH+3, CO+, C3H+3, OH+, H3O+, CH3OH+, C3H+4, C2H+2, C2H+, HCO+, S+, CH+3, H2S+, O+, C+, CH+4, C+2, and O+2) are discussed in this paper. At radial distances <1000 km, the electron density is mainly controlled by 6 ions, viz., NH+4, H3O+, CH3OH+2, H3S+, H2CN+, and H2O+, in the decreasing order of their relative contribution. However, at distances >1000 km, the 6 major ions are H3O+, CH3OH+2, H2O+, H3CO+, C2H+2, and NH+4; along with ions CO+, OH+, and HCO+, whose importance increases with further increase in the radial distance. It is found that at radial distances greater than ∼1000 km (±500 km) the major chemical processes that govern the production and loss of several of the important ions in the inner coma are different from those that dominate at distances below this value. The importance of photoelectron impact ionization, and the relative contributions of solar EUV, and auroral and photoelectron ionization sources in the inner coma are clearly revealed by the present study. The calculated ion mass densities are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km. There is a reasonable agreement between the model calculation and the Giotto measurements. The nine major peaks in the IMS spectra between masses 10 and 40 amu are reproduced fairly well by the model within a factor of two inside the ionopause. We have presented simple formulae for calculating densities of the nine major ions, which contribute to the nine major peaks in the IMS spectra, throughout the inner coma that will be useful in estimating their densities without running the complex chemical models.