Cold Controlled Reactions between Molecular Ions and Radicals

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

In this award, funded by the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program of the Division of Chemistry, Professor Heather Lewandowski of the University of Colorado and her graduate and undergraduate student colleagues are studying the collisions of stable and reactive radical molecules with ions. The unique aspect of this project is that the ions (and sometimes the molecules) have been slowed down to incredibly low velocities. These laboratory conditions mimic the environment in the interstellar medium (ISM). The difficulty of preparing isolated ions and/or molecules with these low energies has precluded any significant experimental work being done to study the chemistry in the ISM; this area of investigation is a virtually uncharted frontier. Studies like this could lead the way to understand what kinds of chemical reactions can take place in the ISM, and serve as extraordinarily sensitive checks of computational models of low energy collisional processes. Students working in the Lewandowski group receive training in a large number of laboratory methods, including vacuum science, electronics, and instrument design and construction. Prof. Lewandowski and her group are also involved in a program with the Advanced Lab Physics Association (ALPhA) to run an ALPhA Immersion course at University of Colorado to assist higher-education instructors in developing a modeling-based approach into existing experiments from the instructors' institution. Prof. Heather Lewandowski and her research group conduct low-energy ion-radical molecule collision dynamics experiments to probe the reactivity of these species. These experiments mimic the conditions in the low-temperature environment of the interstellar medium. Preliminary experiments investigate the reactions of hydrogen and nitric oxide with calcium(+) ions (in a variety of electronic states) cooled in an ion trap. In the most ambitious experiments, the reactions between very slow radical molecules and cooled and trapped molecular ions are studied. The radicals (OH, CH, NH) are created in a molecular beam by laser-photolysis or via pulsed discharge. These radicals are slowed with a series of decelerator electrodes using a new type of continuous-wave decelerator developed in the Lewandowski laboratory. The slowed molecules enter an ion trap (e.g. a linear Paul trap), where they interact with a population of cooled ions. Diagnostics are performed (optical imaging of the ions, destructive time-of-flight mass spectrometry of products, etc.) Ions to be studied include the following: singly-ionized species: acetylene, ammonia, methane, hydroxyl (OH+), and methylidyne (CH+). The Lewandowski research group includes active involvement by undergraduates in authentic research. In addition to her experimental work, Prof. Lewandowski works with ALPhA and postdoctoral fellows from the Physics Education group at University of Colorado to develop and run a workshop to assist significant numbers of higher-education faculty members in incorporating modeling into the educators' own laboratory curriculum.