众所周知，分子云是恒星形成的主要场所。伴随着观测仪器的逐渐升级，时至今日已经约~200~多种分子在星际（星周）环境中被观测到，为人们理解分子云内部的物理化学过程架设了桥梁。为了更好的解释观测的分子丰度，天体化学这门学科应运而生。它通过理论、实验和模拟等手段从物理化学角度给出了分子云内分子演化的过程，为人们揭示了分子在星际空间的演化之谜。我的博士论文主要回顾了两种分子频谱数据的分析方法（转动图和能级布局图方法）和天体化学模拟方面的最新研究进展，总结归纳了我在硕博连续期间对一批大质量恒星形成区中复杂有机分子进行的观测丰度分析，以及对“气体+尘埃”天体化学模型中微观物理内容的改进工作，并对未来可能的研究方向做出了展望。我的主要研究成果和新发现如下：1、采用能级布局图方法对利用亚利桑那射电天文台~10~米亚毫米波望远镜观测的北天区绿色延展天体（~Extend Green objects，缩写为~EGOs~）中的复杂大分子的频谱数据进行了分析，得到了~CH$_3$OH，~CH$_3$OCH$_3$，~HCOOCH$_3$~和~CH$_3$CH$_2$CN~的观测丰度，导出了~EGOs~天体的物理和化学性质，并推论出它们很可能处在大质量恒星形成区演化的早期阶段。我们也将~EGOs~中分子的观测丰度与最新文献中“气体+尘埃”化学模型给出的分子丰度进行了比较，发现现有的“气体+尘埃”化学模型不能很好的解释~EGOs~天体中的分子的丰度和丰度比。这就需要我们建立更加合理的化学模型来给出解释。2、我们自己编写了~Fortran\,90~版本的“气体+尘埃”化学模拟程序，并成功地完成了与文献中~5~个典型物理模型中分子化学丰度演化的定标和比较。3、以往的“气体+尘埃”化学模型中，都简单的假设了尘埃颗粒是静止的。但是根据文献，星际分子云是湍动的，尘埃颗粒相对气体是运动的。为了验证尘埃相对运动效应对化学过程的影响，我们在“气体+尘埃”化学模型中加入了湍动引起的尘埃相对气体的运动效应，发现尘埃运动对不同星际环境中的分子丰度的演化影响是不一样的，这种影响可高达几个量级。尘埃相对运动效应很可能会为未来在观测中区分尘埃运动引起的效应提供帮助，也为我们更好地解释分子观测丰度提供了一个新的方向。4、“气体+尘埃”化学模型都简单地假设了尘埃具有单一的尺寸，然而在星际云中尘埃的尺寸也是具有一定分布的，甚至尘埃的温度也会随尘埃的尺寸变化而变化。为了验证它们对星际化学的影响，在我们新“气体+尘埃”模型中，我们同时考虑了尘埃尺寸分布、尘埃温度分布和与尘埃尺寸密切相关的尘埃吸积离子的过程。研究结果表明，离子吸积和尺寸分布对某些尘埃表面分子丰度的影响很大（可达~2-4~个量级），过去使用的不同尺寸尘埃上分子的面密度一样的假设也变得不再成立，这都说明尘埃吸积离子和尘埃尺寸分布是天体化学模型中的两个重要的影响因素，可能为我们在未来工作中解释~EGOs~中的复杂有机分子的观测丰度提供了新的机会。
其他摘要
As we know, molecular clouds are the main birth places of stars. There are more than 200 molecules have been observed in interstellar space with the enhancements of techniques, which like a good bridge to people to understand the physics and chemistry of molecular clouds. To explain the physical and chemical processes ofthe observed abundances of molecules, the astro-chemistry has been improved from many aspects,such as theories, experiments and modelings, for many years. These efforts are revealing the mystery of history of interstellar molecules. My thesis review two methods (rotation diagram and population diagram analysis) which used to analyze the observed spectral line data of complex organic molecules and the newest status of astro-chemical modeling.This thesis also make a summary of my scientific works during PhD's study on the analysis of observed abundances of complex organic molecules in EGOs and the microcosmic physical improvements to astro-chemical models. A outlook of future works is given in the end.Our main results and new findings are:1. The abundances of CH$_3$OH, CH$_3$OCH$_3$, HCOOCH$_3$ and CH$_3$CH$_2$CN observed in Extend Green objects (EGOs) in northern sky are deduced by using population diagram method. The physical and chemical properties of EGOs are also deduced, which hint that they are in the early-stage of massive star-formation. We also compare the observed abundances with results from gas-grain chemical models and find that the models cannot explain the chemistry in EGOs well. Thus, a more suitable gas-grain chemical model is needed for EGOs.2. We write a new gas-grain chemical code with Fortran\,90 programming language and a benchemarking of our code has been finished successfully with the 5 typical models addressed in literature.3. The dust grains are assumed in quiescent status in previous gas-grain chemical models. However, the molecular clouds are turbulent which result in the relative velocity of dust grain. To check the effects of dust grain motion, we add it to our gas-grain model and test it in different typical interstellar environments. We find that it can alter the abundances of species by factors up to several orders of magnitude, which may help us to differ the dust grain motion via chemical effects and explain the chemistry better from a new view.4. The previous gas-grain chemical model assume that the dust grains have uniform sizes. However, the dust grains have some forms of grain size distribution addressed in literature through observations, even the dust temperatures are also fluctuant. To check the effects of them to chemistry, we take account the dust grain size distribution, fluctuation of dust temperature and ion accretion into our gas-grain model. Our results show that the abundances of some surface-species can be enhanced by 2-4 orders of magnitude and the consumption of constant areal density becomes invalid. Therefore, grain size distribution and ion accretion are important factors to interstellar chemistry, which may provide new change to interpret the observed abundances of molecules in EGOs.
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