Illuminating Molecular Spin Relaxation Mechanisms through Ligand Field Theory and Physical Inorganic Spectroscopy

Citation

Kazmierczak, Nathanael Parker (2025) Illuminating Molecular Spin Relaxation Mechanisms through Ligand Field Theory and Physical Inorganic Spectroscopy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wysm-z777. https://resolver.caltech.edu/CaltechTHESIS:05152025-215940051

Abstract

Electron spin relaxation is a fundamental process in paramagnetic molecules, and successful development of molecular quantum bits (qubits) for quantum information science hinges on suppressing the rate of spin relaxation. While the relaxation process has been studied since the early 20th century, no consensus has been reached regarding the physical relaxation mechanism in S = 1/2 transition metal molecules. Practical guidelines for designing molecules with slow spin relaxation have likewise remained obscure. This thesis describes the use of ligand field theory and physical inorganic spectroscopy techniques to shed new light on molecular spin relaxation mechanisms, connecting relaxation rates to chemical bonding and transition metal electronic structure. Part 1 (Chapters 2-4) details the use of electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and resonance Raman (rR) to interrogate the origins of spin relaxation. Experimental spectroscopic results are analyzed within the context of a model based on group theory, yielding a paradigm referred to as ligand field spin dynamics. Part 2 (Chapters 5-7) describes the development of a new experimental observable, T1 anisotropy, as a novel approach for distinguishing between competing theoretical spin relaxation models. Part 3 (Chapters 8-10) shows how the insights of ligand field spin dynamics and T1 anisotropy have been leveraged to rationally design molecules with slow spin relaxation and other desirable spin dynamics properties. This thesis establishes a framework for controlling the physical process of spin relaxation through distinctly chemical molecular design principles.

Thesis Files