Imaging Frontside and Backside Attack in Radical Ion–Molecule Reactive Scattering

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 127; no. 26; pp. 5565 - 5571
• Main Authors: Ayasli, Atilay, Khan, Arnab, Michaelsen, Tim, Gstir, Thomas, Ončák, Milan, Wester, Roland
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.07.2023
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.3c02856

We report on the reactive scattering of methyl iodide, CH3I, with atomic oxygen anions O – . This radical ion–molecule reaction can produce different ionic products depending on the angle of attack of the nucleophile O – on the target molecule. We present results on the backside and frontside attack of O – on CH3I, which can lead to I – and IO – products, respectively. We combine crossed-beam velocity map imaging with quantum chemical calculations to unravel the chemical reaction dynamics. Energy-dependent scattering experiments in the range of 0.3–2.0 eV relative collision energy revealed that three different reaction pathways can lead to I – products, making it the predominant observed product. Backside attack occurs via a hydrogen-bonded complex with observed indirect, forward, and sideways scattered iodide products. Halide abstraction via frontside attack produces IO – , which mainly shows isotropic and backward scattered products at low energies. IO – is observed to dissociate further to I – + O at a certain energy threshold and favors more direct dynamics at higher collision energies.