分子云坍缩期间星际前生物分子演化的水化学研究
Hydro-chemical study of the evolution of interstellar pre-biotic molecules during the collapse of molecular clouds
摘要：
研究星际分子演化的障碍之一是对发生在星际介质和分子云中的各种反应的速率系数缺乏足够的了解。在计算复杂的前生物分子丰度的文献中确实存在一些速率系数的理论模型。到目前为止，这些已经被用来研究这些分子在太空中的丰度。然而，为了获得更准确的最终组成，在这些介质中，我们找到了一些最重要的星际前生物分子的形成速率系数，通过使用量子化学理论。我们在水化学模型中使用这些速率来找出原恒星坍缩阶段的化学演化和前生物物种的最终丰度。我们发现，在原恒星的坍缩阶段，可以产生大量的各种前生物分子。我们广泛研究了这些分子通过连续的中性-中性和自由基-自由基/自由基-分子反应的形成。我们提出的时间演变的化学物种，重点是如何生产这些分子随云的深度而变化。我们比较腺嘌呤在星际空间中的形成，使用我们的速率系数，并使用从现有的理论模型中获得的。发现益生元分子的形成途径高度依赖于反应物种的丰度和反应中涉及的速率系数。颗粒的存在强烈地影响气相物种的丰度。我们还进行了不同的途径之间的比较研究，可用于腺嘌呤，丙氨酸，甘氨酸和其他分子的合成考虑在我们的网络。
英文摘要：
One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge of the rate co-efficients of various reactions which take place in the Interstellar medium and molecular clouds. Some of the theoretical models of rate coefficients do exist in the literature for computing abundances of the complex pre-biotic molecules. So far these have been used to study the abundances of these molecules in space. However, in order to obtain more accurate final compositions in these media, we find out the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical theory. We use these rates inside our hydro-chemical model to find out the chemical evolution and the final abundances of the pre-biotic species during the collapsing phase of a proto-star. We find that a significant amount of various pre-biotic molecules could be produced during the collapsing phase of a proto-star. We study extensively the formation these molecules via successive neutral-neutral and radical-radical/radical-molecular reactions. We present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud. We compare the formation of adenine in the interstellar space using our rate-coefficients and using those obtained from the existing theoretical models. Formation routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the reactions. Presence of grains strongly affect the abundances of the gas phase species. We also carry out a comparative study between different pathways available for the synthesis of adenine, alanine, glycine and other molecules considered in our network.
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