Low Temperature (1-300 K) Chemistry and Collision Dynamics Relevant to Planetary Atmospheres, Comets and the ISM

亚利桑那大学的Mark A. Smith在实验物理化学项目的支持下，继续研究1 - 300K温度下气相化学反应的机理和动力学。主要目标是进一步了解极低能量碰撞现象，并获得模拟行星大气、彗星、星周和星际化学环境所需的绝对反应速率和产物分支比。他将使用基于自由射流的流动反应器研究1K附近的自由基-分子和分子-分子碰撞过程，并使用激光诱导荧光和基于质谱仪的拉瓦尔流动反应器在广泛的温度和压力范围内测量速率、分支比和产物特性。这些研究的宽温度范围包括星际云中普遍存在的温度范围，并且许多要研究的反应在该环境中特别重要。例如，在这些区域，分子中的氘原子增强，这可能是由于颗粒机制，离子-分子反应途径中的分馏或中性分馏。必须研究反应，以确定哪种替代方案是可行的。我们对低能分子间相互作用的一般认识很差，因为以前还没有实验方法允许在低于250K的温度下进行研究。这些研究将在低温物理化学领域开辟新天地。

Mark A. Smith of the University of Arizona is supported by the Experimental Physical Chemistry Program to continue his studies on the mechanism and dynamics of gas phase chemical reactions at temperatures between 1 and 300K. The primary goal is to further the understanding of very low energy collision phenomena and to obtain absolute reaction rates and product branching ratios needed for the modeling of planetary atmospheric, cometary, circumstellar and interstellar chemical environments. He will investigate radical-molecule and molecule-molecule collision processes near 1K using a free jet-based flow reactor, and measure rates, branching ratios and product identities over a wide range of temperatures and pressures using laser-induced fluorescence-based and mass spectrometer-based Laval flow reactors. The wide temperature range of these studies encompasses those prevalent in interstellar clouds, and many of the reactions to be investigated are particularly important in that environment. For example, there is an enhancement of deuterium atoms in molecules in these regions, which may be due to grain mechanisms, fractionation in ion-molecule reaction pathways or neutral fractionation. Reactions must be studied to determine which alternative is viable. Our general knowledge of intermolecular interactions at low energies is poor because experimental methods have not previously existed to permit studies at temperatures below about 250K. These studies will break new ground in physical chemistry at low temperatures.