Laboratory measurements of three deuterium substitution reactions important in interstellar chemistry

占据星际空间的极冷而稀薄的气体和尘埃云--恒星之间的空间--蕴含着丰富的化学物质。这项研究项目将研究驱动星际气体化学的最简单的多原子分子离子的化学反应。这些离子可以在极低的温度下存在，而大多数其他分子在这种温度下会冻结。研究小组将使用复杂的实验室实验来准确确定离子在极低温度下的反应速度。这项研究的结果将使天文学家能够更好地了解这些离子在太空中的丰度，并将它们用作星际云中最冷、最密集区域的探测器，星际云是恒星和行星的诞生地。该项目将有助于博士后学者的培训和专业发展。该项目还将支持一个被认为对初中和高中科学教育产生积极影响的项目。研究小组将对氢原子与氢的气相反应进行实验室研究。氢是星际气体中发现的最简单的多原子离子，以及它的氚化态H2D+和D2H+。这三个反应在化学反应中很重要，这会显著增加星际分子中的氘含量；而h2d+和d2h+离子探测到冷暗云中密度最高的区域，那里大多数其他分子都被冻结了。因此，了解这些离子的化学对于理解这些区域是至关重要的，这些区域是恒星和行星形成的潜在地点。拟议的研究具有挑战性，因为原子和分子离子很难在实验室中生产。该团队将使用双源合并快束装置测量D原子与H3+、H2D+和D2H+反应的速率系数，该装置由美国国家科学基金会先前的支持(AST-0905832)建造，使它们能够产生原子束和分子离子束并进行反应。从测量的速率系数中提取的碰撞截面将被用来产生与冷星际云(10K-100K)相关的温度下的热速率系数。预计速率系数的精确度将在15%以内--大约比三个反应的计算值高出一个数量级。该项目将支持哥伦比亚大学的一名博士后学者。该项目还将允许团队成员继续参与哥伦比亚大学暑期研究项目，该项目吸引初中和高中教师参与科学研究，并已被证明有助于留住学校的教师，提高学生在科学课程中的表现。

The extremely cold and tenuous clouds of gas and dust that occupy interstellar space -- the space between the stars -- host a rich chemistry. This research project will study chemical reactions of the simplest polyatomic molecular ions that drive the chemistry of the interstellar gas. These ions can exist at the very low temperatures at which most other molecules freeze out. The research team will use a sophisticated laboratory experiment to accurately determine reaction rates of the ions at very low temperatures. Results from the study will allow astronomers to better understand the abundance of these ions in space and to use them as probes of the coldest and densest regions within interstellar clouds, which are birthplaces of stars and planets. The project will contribute to the training and professional development of a postdoctoral scholar. The project will also support a program that is known to have a positive impact on middle school and high school science education.The research team will perform laboratory studies of the gas-phase reactions of atomic deuterium with H3+ -- the simplest polyatomic ion found in the interstellar gas -- and its deuterated forms H2D+ and D2H+. The three reactions are important in the chemistry that drastically increases the deuterium content of interstellar molecules; and the H2D+ and D2H+ ions probe the densest regions of cold dark clouds where most other molecules freeze out. Understanding the chemistry of these ions is therefore essential to understanding these regions, which are potential sites of star and planet formation. The proposed studies are challenging because atoms and molecular ions are difficult to produce in the laboratory. The team will measure rate coefficients of the reactions of D atoms with H3+, H2D+, and D2H+ using a dual-source, merged fast-beams apparatus, which was built with prior NSF support (AST-0905832), that enables them to produce and react beams of atoms and molecular ions. Collisional cross sections extracted from the measured rate coefficients will be used to generate thermal rate coefficients at temperatures relevant to cold interstellar clouds (10 K - 100 K). The rate coefficients are expected to be accurate to within 15% -- about an order of magnitude better than those calculated for the three reactions. The project will support a postdoctoral scholar at Columbia University. The project will also allow team members to continue participating in the Columbia University Summer Research Program that engages middle school and high school teachers in scientific research, and has been shown to help retain teachers in school and improve student performance in science courses.