Alkyne Combustion: Experimental and Computational Studies of HCO Formation

The United States consumed a total of 97.4 trillion BTUs of energy in 2016 with over 80% of that energy consumption source being fossil fuel combustion. Before a combustion reactions reaches its end products, a number of intermediate products form and may react with other abundant atmospheric species to form aerosol particles and acid rain, both of which have potentially negative impacts on both human-made structures and the natural environment. In an effort to counteract the consequences of fossil fuel combustion, scientists are interested in understanding the reaction mechanisms of hydrocarbon combustion reactions to understand which intermediate products form and how. One of the many intermediate products formed in hydrocarbon combustion reactions if the formyl radical, HCO. Discovered in 1934, HCO has since been proven to form in many hundreds of combustion reactions and plays key roles in both atmospheric and interstellar chemistry, namely as a donor of hydroxyl radicals. While alkane combustion has been studies extensively in the past, alkene and alkyne combustion has received little attention beyond the short-chain species: ethylene, propene, acetylene, and propyne. Due to remaining relatively uninvestigated, the formation of HCO during alkyne combustion reactions is focused on in this project. This thesis provides both an experimental and theoretical perspective on the reactions of atomic oxygen atoms, O(3P), with the alkynes propargyl alcohol and 3-butyn-1-ol. Preliminary experimental studies of alkyne combustion revealed strong variations in HCO absorption intensity across different alkyne species. The most dramatic difference in HCO absorption intensity was observed between the combustion of propyne and propargyl alcohol, where propargyl alcohol gave a much stronger signal for HCO than propyne. Both compounds are three carbon alkynes, with the only difference being the hydroxyl substituent on propargyl alcohol. This study attempts to explain these variations via computational investigation. Utilizing optimization QM methods, potential energy profiles are mapped out to reveal the energetics of reaction pathways that result in the formation of HCO. Isoformyl radical, HOC, is also investigated computationally in this project as it is the higher energy isomer of HCO and may isomerize to the lower energy state. The computational portion of this study reveals a higher number of HCO/HOC formation pathways for the alcohol-substituted alkynes and focused on the reactions of O(3P) + propargyl alcohol and O(3P) + 3-butyn-1-ol. The experimental portion of this study involves the detection of HCO as it forms during alkyne combustion via Cavity Ring-down Laser Absorption Spectroscopy (CRDLAS)