Quantum-State-Selected Ion-Molecule Reaction Dynamics: Effects of Translational, Rotational, Vibrational, Spin-Orbit, and Electronic States on Chemical Reactivity

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In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Cheuk-Yiu Ng of the University of California at Davis is using instruments previously developed in his laboratory to explore how chemical reactions depend on how energy is contained in the reacting molecules. Molecules possess energy according their different modes of motion, for example how they move through space (translational), how they vibrate, and how they rotate. Molecular energy also includes the energy of the electrons within the molecules. Prof. Ng has developed a novel instrument that can produce molecular ions (molecules with negative or positive charge, for example H2O+ or O2+) with precisely known translational, vibrational, rotational, and electronic energies. These "state selected" molecular ions are then reacted with other neutral molecules, and the reaction products then provide insight into how the different types of molecular energy influences their reactivity. Prof. Ng's research may make it possible one day to control chemical reactions based on the distribution of energy within the molecules. This project involves the development of state-of-the-art vacuum ultraviolet (VUV) laser sources and novel laser spectroscopic techniques. As such, the project is providing an excellent education opportunity for training the next generation of researchers in laser spectroscopy and dynamics. The current focus of the experiment is to perform absolute integral cross section measurements for a variety of ion-molecule reactions involving quantum-rovibronic-state-selected ions such as N2+, H2O+, H2+, and O2+. Due to the recent success in preparing vanadium cation in long-lived V+ (a5DJ), V+ (a5FJ), and V+ (a3FJ) spin-orbit and electronic states, Prof. Ng's group also plans to examine quantum-state-selected measurements for the reactions of vanadium ions. The neutral reactants to be included in this study are Ne, Ar, H2, HD, D2, O2, N2, CO, NO, HCN, H2O, D2O, CH4, C2H2, C2H4, C2H6, C3H4, C4H2, C6H6, CH3OH, and NH3. These ion-molecule reactions play a pivotal role in the catalytic function of transition-metal cations complexes and the understanding of the chemistry occurring in planetary atmospheres. The results obtained would also serve as benchmarks for state-of-the-art quantum dynamics calculations.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.