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

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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.