Insight into atmospheric formation of hydroxyl radicals using infrared action spectroscopy

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Anne Schou Reinholdt


DKK 425,000




Internationalisation Fellowships


The objective of this project is to explore the chemistry of hydroxyl radicals (OH) in the troposphere. When ozone adds across the double bonds of alkenes it forms cyclic structures that eventually transform to energised Criegee intermediates (CIs). Some CIs decay instantly to OH while others stabilise collisionally prior to thermal decay. We will study stabilised CIs because they are sufficiently stable to react further with atmospheric gases. In another study, we will investigate the combustion of alkanes, which consumes and regenerates OH. The alkane reacts with OH forming an alkyl radical (R) that subsequently reacts with oxygen producing a carbon-centred hydroperoxide radical intermediate (QOOH) that can decay to release OH.


OH is a key oxidant in the troposphere. Due to its extreme reactivity, it controls the lifetime of organic compounds including greenhouse gases and pollutants. OH typically abstracts a hydrogen atom from an organic compound leading to water-soluble products, which can be removed from the troposphere via rain and snow. The concentrations and sources of OH are therefore highly important, especially for accurate modelling of atmospheric chemistry.


The research will be conducted at the University of Pennsylvania in the group of Professor Marsha I. Lester. Here, stabilised CIs and QOOHs will be synthesised in the gas phase and characterised with infrared (IR) action spectroscopy. This involves pumping energy (IR radiation) into the stabilised intermediates to initiate unimolecular decay that releases OH. The experiments provide IR action spectra of the intermediates and establish the rate of OH release. Theoretical studies will be performed to interpret the experimental observations in terms of isomer- and conformer-specific reaction pathways and barriers for OH production.

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