Unravelling Reaction Pathways for Alkene Ozonolysis and Alkane Oxidation

• Applicant: Dr. Tarun Kumar Roy
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2022 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 508074809

Hydroxyl radicals (OH), often called the “atmosphere's detergent”, initiate the oxidation of most volatile organic compounds in the troposphere. The reaction pathways for production of OH radicals are important for accurately modeling atmospheric chemistry. The proposed project aims to elucidate two major chemical reaction pathways that produce or regenerate OH radicals in the atmosphere: firstly, alkene ozonolysis, which is an important non-photolytic route to generate OH radicals, and secondly, alkane oxidation that both consumes and regenerates OH radicals. Alkene ozonolysis proceeds through zwitterionic carbonyl oxide reactive intermediates, called Criegee intermediates, while alkane oxidation forms transient carbon-centered hydroperoxyalkyl radicals (•QOOH), which are a critical junction in the oxidation mechanism but have generally eluded direct experimental observation. The purpose of this project is to explore various Criegee intermediates and •QOOH radicals in order to characterize them spectroscopically and investigate their novel chemical reaction pathways. Experimentally, an IR pump-UV probe scheme will be employed to investigate the IR spectroscopy and unimolecular decay rates of these intermediates under controlled laboratory conditions. Furthermore, using a combination of 1+1' resonance-enhanced multiphoton ionization (REMPI) scheme and velocity map imaging (VMI) approaches, the unimolecular dissociation dynamics of •QOOH intermediates will be investigated. The experimental results will be complemented by calculated vibrational spectra of the intermediates and accompanying kinetic rate calculations. The findings of this project will yield new insights on the unimolecular reaction pathways of Criegee intermediates and •QOOH radicals leading to OH products.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professorin Dr. Marsha Lester