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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FCSpecTRe (Frequency Comb Spectroscopy of Temperature-dependent Reactions)

Teaser

Summary

Gas phase chemical reactions are often monitored by the studying the loss of a reactant or growth of a product. For example, an infrared laser can be used in direct absorption techniques. If infrared light is incident on a gaseous sample where one of the molecules (reactant or product) absorbs light at that particular frequency by exciting a vibration, then the light intensity is attenuated. However, this technique is usually a highly specialized technique and specific to a single molecule since the laser used operates at a single narrow frequency. A new direct absorption spectrometer has been built in my lab using a broadband and high resolution mid-infrared light source, called a frequency comb laser. Any molecule that absorbs mid-infrared light can be monitored in this spectrometer, and with the high spectral resolution, molecules can be distinguished from one another. In this way, this spectrometer has molecular specificity but is also general to a wide range of molecules and so it can simultaneously monitor the loss of reactant and growth of a product during a chemical reaction. In addition, the spectrometer has rapid detection and high sensitivity, so it is able to monitor these molecules as a function of time to measure rates of reactions and is able to see very small, trace amounts of molecules formed. Many models of Earthâ€™s atmosphere use information from complex chemical reactions to build up an understanding of the overall chemistry occurring. The multiplexed data on chemical reaction kinetics achieved with this spectrometer contributes a significant amount of information to these models, making them a more accurate representation of the chemistry occurring. The overall objectives of this project were to build a new spectrometer with dual detection techniques, fully characterize and optimize its performance, and apply this to the gas phase chemistry and spectroscopy of CH radical reactions. A significant part of the fellowship is also to undergo a series of training objectives to enable my transition into a fully independent, successful scientist, mentor of young scientists, and academic leader in my field.

Work performed

A new frequency comb spectrometer was built using two detection techniques: a spatially dispersive method and a time-domain method for direct absorption spectroscopy. These two detection techniques have been fully optimized and characterized using the spectroscopy of methane. Significant amounts of software has been written to quickly collect and analyse the large quantities of data being generated during any one experiment. In addition, work towards the photolysis of bromoform, an important CH radical source, has been underway using the cutting edge technology developed in this fellowship. The results during the fellowship period have been summarized in a series of student reports and disseminated to scientific audiences through several invited and contributed talks at international and UK conferences. Results throughout the project were also disseminated to the wider public through my newly created Twitter account, with â€œlab shot of the dayâ€ photos of results alongside a general summary.

Final results

The spatially dispersive frequency comb spectrometer is the first of its kind in the UK and Europe, to the best of my knowledge, and the first in the world to achieve its enhanced resolution. It is also the first in the world to exist outside of a primarily physics department. This represents an advancement in the state of the art, and a significant step in integrating advanced physics techniques into a chemistry research program. Beyond the scientific state of the art and its impacts, there have been a significant amount of potential impacts on myself as an early career researcher and the numerous students I have mentored during this project.