Ion-Radical Chemistry in a Controlled Experiment

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In this project funded by the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) Program of the Chemistry Division, Professor Heather Lewandowski and her research group at the University of Colorado at Boulder is using laser cooling and trapping techniques to study chemical reactions between molecular ions and neutral free-radical molecules. Molecular ions are molecules that are either missing electrons (and therefore are positively charged) or have extra electrons (making them negatively charged). Neutral free-radical molecules are not charged, but have electrons that are unpaired. The charge on a molecule and whether or not it has unpaired electrons greatly influences the chemical reactivity of the molecule. The Lewandowski laboratory has developed laser cooling and ion trapping instruments that can precisely control the speed and energy with which the ions and radicals collide. The ability to control collisions allows the team to evaluate how charge and unpaired electrons affect the speeds and outcomes of chemical reactions. This work bridges the communities of molecular physics, physical chemistry, and astrochemistry. The students working on this project gain valuable knowledge and skills in advanced laser optical techniques and computational chemistry.This project focuses on determining reaction rates and mechanisms for reactions between sympathetically cooled molecular ions trapped in a radio-frequency trap and a neutral free radical molecular beam decelerated using time-varying inhomogeneous electric fields. Typically, neutral molecules include OH, CH and NH3, while the ion species are varied to study a large range of astrophysically- and atmospherically-relevant reactions. After a reaction experiment has taken place, all of the ions in the trap, including all product ions, are ejected into a time-of-flight mass spectrometer for mass-to-charge identification. By varying the reaction time, the reaction rate is determined. The experimental data are interpreted with the help of high-level theoretical calculations of the potential energy surface. The broader impacts of this work include training of students in interdisciplinary research using both molecular physics and physical chemistry techniques and perspectives.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.