Experiment and Modeling Combined Kinetic Study of Bottom-up Polycyclic Aromatic Hydrocarbon Formations

Abstract

Despite their importance, the chemical mechanisms of polycyclic aromatic hydrocarbon (PAH) formation are not well understood. Therefore, a combined theoretical and experimental study of the chemical kinetics PAH formation is essential to deepen our understanding to draw a complete picture of aromatic chemistry. This thesis includes both modeling and experimental works on PAH formations from small molecules. Through a combination of high-level quantum chemistry calculations, reaction rate coefficients calculation, and simulation of reactions, bottom-up PAH formation chemistry was predicted and understood. This model prediction can be validated and improved when combined with advanced experimental techniques using a unique apparatus that consists of a quartz reactor combined with time-of-flight mass spectrometry. Chapter 2 focuses on experimentally validating model-predicted tricyclic PAH (phenanthrene and anthracene) formations through the HACA mechanism during the (1, 2-) naphthalenyl radical + acetylene reaction at temperatures between 500–800 K and pressures between 15-50 Torr. We measure significant quantities of C14H10 for the first time, as well as C12H8 from 2-naphthalenyl radical + acetylene. We also explain the discrepancy between our experimental study and the previous experiment performed by Parker et al. that couldn’t detect C14H10. Chapter 3 focuses on the investigation of the benzyne-related chemistry (both benzyne + benzene and benzyne + toluene) to validate its ability to rapidly form PAHs through -bond 1,4-cycloaddition/fragmentation (1,4-CAF), which was predicted by the kinetic model. We measure C10H8 and C12H10 as well as its kinetics from benzyne + benzene at 800 K and 30 Torr. We measure C10H8, C11H10, and C13H12 from benzyne + toluene at 800 K and 30 Torr. These results provide the first direct experimental evidence for rapid molecular growth through -bond 1,4-CAF of o-benzyne to C6 aromatic hydrocarbons. In chapter 4, preliminary kinetic modeling of the PAH formation of toluene (+benzene) pyrolysis at one experimental condition (1467 K, 10.02 Torr, up to 0.56 s) is reported to describe major product peaks observed from Shukla et al. using the reaction mechanism generator.16 Chapter 5 shows a recommended future application of the knowledge learned from this thesis to astrochemistry. Overall, the studies here show a successful investigation of bottom-up PAH formation through experimental and theoretical approaches.Ph.D