New Technology for Exploring State-Dependent Reactivity in Radiative Association Reactions

在这个由化学系化学结构、动力学和机理（CSDM-A）项目资助的项目中，马里兰州大学的Leah Dodson教授和她的学生将研究原子金属离子与一类中性分子氰基多炔的反应性。与传统的化学反应相反，这些反应的速率预计会随着温度的降低而增加;然而，这种反向的温度依赖性在实验室中测量具有挑战性。通过设计新的仪器来在低温下制备反应物并通过质谱法直接检测来测量反应性，将克服实验挑战。结果将提供洞察一类反应发生在寒冷的天体物理对象和测试理论预测在一个基本的水平。研究生和本科生将参与这项多学科研究，该团队将与附近的乔治王子社区学院的教师密切合作，为副学士学位课程的学生提供研究机会，其中许多人是代表性不足的群体的成员。这项工作的更广泛的影响将包括离子/分子辐射缔合反应的更完整的图片，邀请与理论化学家合作，并有助于行星和恒星演化的理解。该项目将开发必要的低温冷却技术，以研究低温（低至10 K）下的离子/分子辐射缔合反应。预测金属一价阳离子（如镁）和氰基多炔的辐射缔合具有强烈依赖于中性反应物的旋转能和偶极矩的速率。为了直接测量与温度相关的速率，冷离子和分子将在反应之前独立产生。气态金属原子离子将在辉光放电离子源中产生，并在低温多极离子阱中被捕获和冷却。氰基聚炔中性反应物在注入离子阱之前将在缓冲气体碰撞池中冷却。动力学数据将从随时间变化的离子信号中获得。反应物的旋转能和偶极矩的测量速率常数的依赖性将提供必要的独立数据来测试理论方法之间的差异，目前差异高达四个数量级。该项目将通过新技术的开发和对专业发展的关注，为科学、技术、工程和数学方面的研究生、本科生和副学士学生提供培训机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

In this project, funded by the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) program of the Chemistry Division, Professor Leah Dodson and her students at the University of Maryland will study the reactivity of atomic metal ions with a class of neutral molecules—cyanopolyynes. Contrary to conventional chemical reactivity, the rates for these reactions are expected to increase as temperature decreases; however, this inverted temperature dependence is challenging to measure in the laboratory. The experimental challenges will be overcome by devising new instrumentation to prepare reactants at low temperatures and measure reactivity through direct detection by mass spectrometry. The results will provide insight into a class of reactions occurring in cold astrophysical objects and test theoretical predictions at a fundamental level. Graduate and undergraduate students will be involved in this multidisciplinary research, and the team will collaborate closely with faculty from nearby Prince George’s Community College to provide research opportunities for students in their associate degree program, many of whom are members of underrepresented groups. The broader impacts of this work will include a more complete picture of ion/molecule radiative association reactions that invites collaboration with theoretical chemists and contributes to the understanding of planetary and stellar evolution. This project will develop the cryogenic cooling techniques necessary to study ion/molecule radiative association reactions at low temperatures (down to 10 K). The radiative association of metal monocations (such as magnesium) and cyanopolyynes is predicted to have a rate that depends strongly on the rotational energy and dipole moment of the neutral reactant. To directly measure the temperature-dependent rates, the cold ions and molecules will be produced independently prior to reaction. Gaseous atomic metal ions will be generated in a glow-discharge ion source and trapped and cooled in a cryogenic multipole ion trap. The cyanopolyyne neutral reactant will be cooled in a buffer-gas collision cell before being injected into the ion trap. Kinetics data will be obtained from the time-dependent ion signals. The dependence of the measured rate constant on reactant rotational energy and dipole moment will provide independent data necessary to test discrepancies between theoretical methods that currently differ by up to four orders of magnitude. The project will provide opportunities for training graduate, undergraduate, and associate degree students in science, technology, engineering, and mathematics through the development of new technologies and a focus on professional development.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.