Improving Models of Molecular Clouds and Planetary Atmospheres: Dissociative Recombination Measurements for Molecular Ions of Astronomical Interest

改进分子云和行星大气模型：天文感兴趣的分子离子的解离重组测量

• 批准号: 1107036
• 负责人: Daniel Wolf Savin
• 金额: $ 55.74万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1107036&HistoricalAwards=false
• 关键词: Improving; Models; Molecular; Clouds; Planetary

The PI and his team will measure dissociative recombination branching ratios and rate coefficients for important chemical molecular ion reactions in cold interstellar clouds. This work on dissociated recombination reaction rates and cross-sections is needed to understand the molecular inventory and cooling of the interstellar medium, and to put astrochemical models onto a firm base.Molecules are key components of diffuse, translucent and dense molecular clouds, hot cores, photon dominated regions, protostellar disks, protoplanetary disks, planetary and satellite ionospheres, cometary comae, and circumstellar envelopes around dying starsModels and interpretations of the chemical composition, charge balance, emission and/or absorption spectra, and thermal structure in the various astronomical environments depend on reliable knowledge of the underlying molecular collisions which control these properties. Among the dissociative recombination reactions the primary neutralizing reactions for molecules in cosmic plasmas are particularly important. Dissociative recombination involving ion-molecule reactions is often the terminating step for particular synthesis pathways in chemical networks. One needs to know rates and branching ratios for final products in order to understand reaction pathways, and to understand whether a compound can be produced in the gas phase or if grain surface chemistry must be invoked. If the end products of dissociative recombination are energetic, they can collisionally heat the plasma; if they are in excited states, they can cool the gas through radiative relaxation.The experiments are done at the unique heavy-ion Test Storage Ring (TSR) facility at the Max-Planck Institute in Heidelberg, Germany. The ions to be studied are HF+, H2F+, CF+, 16O16O+, 18O16O+, HSiO+, CH2O+, and CH3O+. They are selected based on their importance for ground-based spectroscopic observations combined with astrochemical modeling studies. The selected molecules can be stored long enough in TSR to cool to their lowest electronic and vibrational levels, except for 16O16O+ which will electronically relax but lacks a dipole moment and will not vibrationally radiatively relax. The PI and his team will generate total dissociative recombination rate coefficients versus temperature for the lowest vibrational level of each molecule as well as branching ratios for the various possible outgoing final channels. Such and related data will also find applications in other areas of astronomy such as planetary sciences, e.g., for 16O16O+, they may be able to generate these data as a function of vibrational level, which is needed for martian atmosphere studies. This project has an ongoing international collaboration and strong commitment to education and involves offers a research experience to high school teachers in Staten Island in collaboration with the Columbia Summer Research Program for Science Teachers.

PI和他的团队将测量对冷星云中重要化学分子离子反应的分离重组分支比和速率系数。需要进行解离的重组反应速率和横截面的这项工作，以了解星体介质的分子库存和冷却，并将星体模型放在牢固的基础上。MOLECULES是弥漫性，半透明和密集的分子云，热核的关键组成部分，光子统治区域，原始磁盘，原球盘，行星和卫星电离层，彗星comae和围绕垂死的星星围绕化学组成，电荷平衡，发射和/或吸收环境的解释以及各种天文学环境中的垂直恒星的解释以及各种天文结构的解释取决于对控制这些特性的基本分子碰撞的可靠知识。在解离性重组反应中，宇宙等离子体中分子的主要中和反应尤为重要。涉及离子 - 分子反应的解离重组通常是化学网络中特定合成途径的终止步骤。一个人需要了解最终产品的速率和分支比率，以了解反应途径，并了解是否可以在气相中产生化合物，或者必须调用谷物表面化学。如果解离重组的最终产物能量能量，则可以碰撞地加热血浆。如果它们处于激发状态，则可以通过辐射松弛冷却气体。实验是在德国海德堡Max-Planck Institute的独特的重离子测试环（TSR）设施中进行的。要研究的离子是HF+，H2F+，CF+，16O16O+，18O16O+，HSIO+，CH2O+和CH3O+。根据它们对地面光谱观测的重要性，并与天体化学建模研究相结合。所选分子可以在TSR中存储足够长的时间，以使其冷却至最低的电子和振动水平，除了16o16o+将以电子方式放松，但缺乏偶极矩，并且不会在振动上放松。 PI和他的团队将在每个分子的最低振动水平以及各种可能的传出最终通道的最低振动水平以及分支比率中生成总分离重组率系数与温度。这些和相关的数据还将在其他天文学领域（例如行星科学）中找到应用，例如，对于16o16o+，它们可能能够生成这些数据作为振动水平的函数，这是火星大气研究所需的。该项目在国际合作和对教育方面的坚定承诺和强大的承诺，并与史坦顿岛的高中教师提供了研究经验，并与哥伦比亚科学教师的夏季研究计划合作。