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 Earth’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.
