Semester

Summer

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Fabien Goulay

Committee Member

Kenneth Showalter

Committee Member

Michelle Richards-Babb

Committee Member

Stephen Valentine

Committee Member

Talitha Selby

Abstract

The formation of polycyclic aromatic hydrocarbons (PAHs) and carbon-based nanoparticles in combustion environments is driven by the pyrolysis and oxidation of abundant fuel molecules. The subsequent growth of these pyrolytic byproducts is then propagated by reactions with small free radical species like OH, CH, O atoms, and C2H. Cyclopentadiene (C5H6) is a significant five-member combustion intermediate that has been detected in many high temperature reactions, such as in the pyrolysis of jet fuels like JP-10. Experimental and theoretical investigations in the reactions of cyclopentadiene with these small free radical species are necessary towards understanding the initial rate-limiting steps in the overall PAH growth scheme. Experimental kinetic rate constants are obtained for the CH radical reaction with cyclopentadiene under pseudo-first order conditions in a quasi-static reaction cell. The CH radical is generated by pulsed laser photolysis (PLP) of bromoform (CHBr3) at 266 nm and the concentration is monitored using laser-induced fluorescence (LIF) at an excitation wavelength of 430 nm. Isomeric products and associated branching ratios are measured for CH and OH radical reactions with cyclopentadiene using multiplexed photoionization time-of-flight mass spectrometry coupled to synchrotron radiation at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratories in Berkeley, California. Density functional theory and CBS methods are used to calculate the potential energy surface for mechanistic discussions of the previous reactions. Master Equation calculations using the MESMER open-source program are performed to infer product branching ratios about the respective products. Evidence supports a fast, barrierless cycloaddition of the CH radical along the pi-bonds of the five-member ring to form C6H6 isomers (benzene, fulvene, among others) and a H atom. Preliminary results from the OH radical reactions suggest the main pathway follows association to form C5H6OH isomer intermediate thoroughly a weakly bonded van der Waal’s complex. This intermediate can be stabilized at higher pressures or undergo H atom loss to form the final products, C5H5OH.

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