Electron Spin Decoherence in Glassy Matrices

Abstract

Electron spin coherence is the ensemble property of multiple electrons, where their spin states maintain a constant phase relationship. In pulse electron paramagnetic resonance experiments, the electron spin co herence is proportional to the detected signal. In this thesis, we discuss our investigations into the role of the environmental nuclear spins, when the electron is on an organic radical solvated in a frozen glassy matrix. Chapters 0–3 introduce the required background and context. In particular, chapter 2 introduces Yang and Liu’s Cluster Correlation Expansion (CCE) [1, 2]. Chapters 4–7 contain the main body where the data is analyzed and discussed; finally, chapter 8 discusses CluE, the home-built software used for the CCE electron spin decoherence simulations of this work. CluE uses structures generated via molecular dynamics to predict electron spin decoherence behavior. We validated CluE simulations against experimental data, and then used in silico structures to determine how different structural features affect electron spin decoherence. Chapter 4 assigns a decoherence contribution to individual nuclei, and identifies the 4–12 Å from the electron as the range where nuclei contribute the most. Chapter 5 looks at the interplay between decoherence pathways that do and do not refocus under different conditions. This could allow some pulsed electron paramagnetic resonance experiments to improve their signal-to-noise ratio. Chapter 6 looks at the effects of isotopic sub stitution of the water/glycerol matrix protons for deuterons. We find that even when only 1% of the hydrons are protons, the protons still contribute more to decoherence than the 99% deuterons. Additionally, proton clusters contribute more than randomly distributed protons. And Chapter 7 looks at protons within methyl groups. Methyl groups are quantum rotors that are both common, and can have a large influence on electron spin coherence. We investigate the spatial and energetic parameter space: we find that methyl groups drives decoherence most when the methyl groups are 2.5–6 Å away from the electron.