What's In A Name?
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Electron paramagnetic resonance (EPR) and electron spin
resonance (ESR) can be viewed as two alternative names in a family of electron
magnetic resonance (EMR) techniques.
The measurements owe their origin to the magnetic
properties of the electron which, since it has a
magnetic moment (associated with the electron spin),
will interact with an external magnetic field. Simply,
the electron can behave like a small bar magnet when
placed in a magnetic field, trying to align itself
with the external field. It is then possible to cause
the electron to 'flip' from alignment with the external
field, to alignment against the field by irradiation with
suitable microwave electromagnetic radiation. (Gigahertz,
that is 109Hz).
Resonance techniques are generally used to measure
this intriguing phenomenon, with the measurements
finding uses in science topics as diverse as anthropology,
the brewing industry, metalloenzyme biochemistry and
the study of the electronic properties of molecules
and atoms, Like its younger cousin, NMR, nuclear magnetic resonance,
EMR is also developing as an imaging technique for
magnetic resonance imaging (MRI).
EMR Abbreviations now in use |
The ESR Spectroscopy Group of the Royal Society of Chemistry
The formation of our Group as a special interest group within the Chemical Society - in 1969
the Royal Society of Chemistry had not yet been formed -
was first suggested at a meeting in University College Cardiff in December
1968, then formally recognised by the Chemical Society in February 1969, and christened
"E.S.R. Group of the CHEMICAL SOCIETY". Our founding fathers, largely organic and physical
chemists, used 'Electron Spin Resonance' rather than the alternative 'Electron Paramagnetic
Resonance'. Had the founders of the Group been physicists, or had they been the early
Oxford workers on paramagnetic resonance, then
we might have been christened 'The E.P.R. Group of the CHEMICAL SOCIETY'.
A quotation from George Pake's monograph 'Paramagnetic Resonance', is apposite:
"The confusion in magnetic resonance terminology leads us to begin on a somewhat
pedantic note. Our subject is sometimes called electron paramagnetic resonance or
electron spin resonance. Paramagnetic resonance, strictly speaking, refers to the
magnetic resonance of permanent magnetic dipole moments and it encompasses not only
the magnetic resonance of electrons but also nuclear magnetic resonance (NMR) ...
Electron spin resonance is more specific, but it is perhaps inaccurate in its implications
because orbital angular momentum contributes in general to the electron magnetic dipole
moment. Even the famous quenching which occurs for the iron group ions does not stamp out
altogether the orbital angular momentum contribution to the magnetic moment.
Our decision simply to refer to paramagnetic resonance ... is perhaps justifiable on the
grounds that the extensive contributions of the Oxford workers have earned for them the
right to name the subject."
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EMR - Electron Magnetic Resonance
EMR can be used as a generic name for a branch of magnetic resonance
spectroscopy involving 'free' or unpaired electrons. This also
provides a logical connection with nuclear magnetic resonance, NMR.
There is a IUPAC Limited Term Task Group on
Electron Magnetic Resonance Spectroscopy Data - see
JCAMP
The list of abbreviations for techniques associated with
electron measurements is formidable (51) - and still growing - if you have
an abbreviation which I have missed, please contact me:
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