Date of Award

2022

Document Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Pharmaceutical and Chemical Sciences

First Advisor

Balint Sztaray

First Committee Member

Michael McCallum

Second Committee Member

Qinliang Zhao

Abstract

Photoelectron Photoion Coincidence (PEPICO) Spectroscopy studies on two unsaturated hydrofluorocarbons (HFCs), also known as hydrofluoroolefines (HFOs), are presented here. Previously, the Sztáray group has studied the dissociation of trans-1,3,3,3-tetrafluoroprop-1-ene (ElixClean), which is a fourth-generation refrigerant and propellant and has lower global warming potential than its precursors. My study is an extension of the ElixClean study as it aims to explore how the different number of fluorine atoms impact the dissociation reactions of these molecules. Both 3,3,3-trifluoropropene (TFP) and cis-1,2,3,3,3- pentafluoropropene (PFP) are also utilized as propellants and refrigerants.Measurements were carried out with remote access to the CRF-PEPICO (combustion reactions followed by photoelectron photoion coincidence spectroscopy) endstation of the vacuum-ultraviolet (VUV) beamline at the Swiss Light Source (SLS). Gas phase samples were intersected with tunable vacuum ultraviolet synchrotron light to create photoions and photoelectrons which are then detected in coincidence. Breakdown diagrams were then obtained by integrating the photoelectron-photoion coincidence signal for times of flight corresponding the precursor and fragment ions and plotting their fractional abundances at each photon energy. Analysis of these dissociation mechanisms was aided by ab initio calculations.

Dissociative photoionization of TFP was studied over the photon energy range of 11.8–16.0 eV. Besides the molecular ion (m/z 96), there were four main fragment ions detected: m/z 95 (H-loss), 77 (F-loss), 46 (CF2-loss), 27 (CF3-loss). The experimental data for the dissociative photoionization of PFP was taken over the photon energy range of 12.0–16.5 eV and indicated the formation of m/z 113(F-loss), m/z 82 (CF2-loss), m/z 69 (C2HF2-loss), and m/z 51 (C2F3-loss), but an H-loss is not detected.

Quantum-chemical calculations at the B3LYP level were used to explore the potential energy surface and identify the most likely structures that play a role in the dissociative photoionization processes of these fluorinated propenes. The energies of the most relevant stationary points were refined utilizing G4 composite method. The dissociation/isomerization pathways of energy-selected TFP and PFP ions will be explored, and I will discuss the most likely mechanisms that lead to the lowest-energy products.

Pages

75

Share

COinS