CRC: Chemistry of Unsaturated Hydrocarbons in Titan's Atmosphere

Ralf Kaiser（夏威夷大学）、Alexander Mebel（佛罗里达国际大学）和Arthur Suits（韦恩州立大学）共同资助了一项研究项目，探索低温环境下不饱和烃的形成和生长机制。他们将与雷恩大学（法国）的伊恩·西姆斯（Ian Sims）合作，使用一系列技术，包括电子结构理论、多质量离子成像、交叉束实验和动力学研究，来解开乙基自由基反应，这些反应将深入了解泰坦、原始地球和富含碳氢化合物的行星及其外太阳系卫星的大气化学。研究目标包括：1)利用无碳氢化合物交叉分子束机研究单碰撞条件下导致碳氢化合物生长的依赖于碰撞能量的反应动力学；2)阐明无碰撞条件下烃类分子的光解动力学，识别所有产物和分支馏分；3)通过在超冷气体准直流中进行反应，揭示乙基自由基与不饱和烃分子的低温动力学；4)与Joel Bowman （Emory大学）合作，利用从头算/统计理论计算在大范围碰撞能量、温度、压力和波长下研究乙基自由基反应和光解过程，并在观察到非统计效应的系统中进行额外的动力学研究；5)与Yuk Yung（加州理工学院）合作，将这些发现应用于化学反应网络，模拟土卫六大气中的碳氢化合物生长，并将模型预测与卡西尼-惠更斯号土卫六任务的公开数据以及合作者Alan Tokunaga（夏威夷大学）提供的天文观测结果进行比较。然后，这些模型可以进一步完善，直到预测和观测到的土卫六大气中碳氢化合物分子的浓度达到一致，并对潜在的化学成分形成一致的认识。乙基、C2H等碳氢化合物自由基是行星及其卫星（如土卫六）富含碳氢化合物的大气中重要的高活性中间产物。通过在实验室环境中了解这些自由基的化学动力学和反应，以及研究碳氢化合物分子的光化学，我们将深入了解土卫六（土卫六是土星的一颗卫星，具有致密的低温、氮和甲烷大气）上有机雾霾层的化学成分以及该大气的演变。该项目的其他更广泛的影响包括反应动力学和天体化学的跨学科培训，科学研讨会，以及培训不同群体的初级研究人员。一个公共网站将提供虚拟实验室之旅，以及化学反应动力学和天体化学领域的介绍。本项目由化学合作研究（CRC）计划和国际科学与工程办公室资助。

Ralf Kaiser (University of Hawai'i), Alexander Mebel (Florida International University) and Arthur Suits (Wayne State University) are jointly supported for a research project exploring the formation and growth mechanisms of unsaturated hydrocarbons in low temperature environments. In collaboration with Ian Sims, University of Rennes (France) they will use an array of techniques including electronic structure theory, multimass ion imaging, crossed beam experiments, and kinetic studies to unravel ethynyl radical reactions under conditions that will give insight into the atmospheric chemistry on Titan, proto Earth, and hydrocarbon-rich planets and their satellites in the outer Solar System. The multi-faceted research goals include 1) to investigate the collision energy dependent reaction dynamics leading to hydrocarbon growth under single collision conditions employing a hydrocarbon-free crossed molecular beams machine; 2) to elucidate the photodissociation dynamics of hydrocarbon molecules under collision-free conditions, identifying all products and branching fractions; 3) to reveal the low temperature kinetics of ethynyl radical reactions with unsaturated hydrocarbon molecules by carrying out the reactions in a collimated flow of ultra-cold gas; 4) to use ab initio/statistical theory calculations to investigate ethynyl radical reactions and photodissociation processes over a broad range of collision energies, temperatures, pressures, and wavelengths, and in those systems where non-statistical effects are observed, to pursue additional dynamics studies in collaboration with Joel Bowman (Emory University); and 5) to apply these findings to chemical reaction networks in collaboration with Yuk Yung (Caltech), modeling the hydrocarbon growth in the atmosphere of Titan and comparing the model predictions with publicly available data from the Cassini-Huygens mission to Titan and with astronomical observations provided by collaborator Alan Tokunaga (University of Hawai'i). The models can then be refined until an agreement between predicted and observed concentrations of hydrocarbon molecules in Titan's atmosphere is reached and a coherent picture of the underlying chemistry emerges. Hydrocarbon radicals such as ethynyl, C2H, are important, highly reactive intermediates in hydrocarbon-enriched atmospheres of planets and their moons such as Titan. By understanding the chemical dynamics and reactions of these radicals in a laboratory setting, and by investigating the photochemistry of hydrocarbon molecules, insight will be gained into the chemistry of the organic haze layers on Titan (a moon of Saturn with a dense cold, nitrogen and methane-based atmosphere) and the evolution of that atmosphere. Other broader impacts of this project include interdisciplinary training in reaction dynamics and astrochemistry, scientific workshops, and training of a diverse group of junior researchers. A public web site will offer virtual laboratory tours as well as an introduction to the fields of chemical reaction dynamics and astrochemistry. This project is funded by the Collaborative Research in Chemistry (CRC) Program and the Office of International Science and Engineering.