EPR / ESR Spectroscopy
This is the main instructional portal for EPR/ESR spectroscopy at Monmouth College. EPR (Electron Paramagnetic Resonance) is also referred to as ESR (Electron Spin Resonance). At Monmouth College, the EPR program is lead by Professor Bradley E. Sturgeon. Brad was first exposed to EPR in the undergraduate chemistry laboratories at Illinois State University in ~1986. In Professor Stevenson's Physical Chemistry Lab students were required to develop glassblowing skills in order to make an apparatus to generate the naphthalene radical anion. ~30 years of EPR/ESR experience, researcher who study the unpaired electrons in organic/carbon-based molecules generally use the term ESR, whereas those who study unpaired electrons in metals use the term EPR. Some believe that the term ESR is outdated and that the term EPR should be used exclusively. Since my research experience involves the study of unpaired electrons in both organic and inorganic compounds, i use either term mainly based on the above definition.
Introduction
The electron is a partless-part that is integral to all molecular structure. As taught in general chemistry, element are defined in terms of the number of protons (the atomic number, Z); these elements also have an equivalent number of electrons hence balancing the charge. Also taught in general chemistry is the octet rule, which states that elements prefer 8 electrons in their outer shell. Because electrons in metals and non-metals behave slightly different, this is the origin of the terms EPR and ESR.
Non-metals
Non-metals like C, N, O, and F each associate with other elements in order to obtain an electron configuration of the noble gases. For example, fluorine has 7 protons and 7 electrons and in order to obtain an electron configuration of Ne (8 e-), it must associate with one element that can provide a single electron. Hydrofluoric acid (HF) results when hydrogen associates with a fluorine atom. Additionally, a fluorine atom can associate with a second fluorine atom to result in molecular fluorine (F2). All halogens appear in their elemental form as diatomic, as do O2, N2, and H2.
Metals Metals like Mn, Fe, Cu, and Ni each associate with other elements in order to stabilize their electron configuration, although since this elements involve a more complex array of shells, the electron configuration is a bit more complicated. For example, manganese has an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d5.
Stable molecular compounds have all electrons paired. In only a small number of cases do
Spectroscopy Basics
