What is ESEEM?

ESEEM stands for Electron Spin Echo Envelope Modulation, and is an experimental magnetic resonance effect which can be observed in pulsed electron paramagnetic resonance experiments.

Nuclear Magnetic Resonance (NMR) spectrometers have for years been built around the idea that powerful pulses of short duration may be used to perturb a sample's magnetization and thereby produce measurable effects which arise from the nuclear magnetic resonances in the sample. This instrument design paradigm has also existed in Electron Paramagnetic Resonance (EPR) spectroscopy, but, to a much lesser extent owing to the difficulties in producing precisely timed pulses and achieving time-resolved data acquisition on the timescales necessary in EPR (up to 1000 times faster than NMR timescales).

The IERC maintains a pulsed EPR spectrometer which operates in the S-Band (2-4 GHz). This instrument was designed and built in the late 1980's. In its initial design, it was capable of producing two- or three-pulse sequences and was capable of 0,180 degree phase cycling.

This machine is used most often to observe the electron spin echo in a paramagnetic system as a function of the time that separates the pulses causing the echo. This technique is called electron spin echo envelope modulation (ESEEM), and is a powerful probe of the radial distribution of magnetic nuclear spins in the environment of the electron spins producing the echo.

We are currently applying the finishing touches to an upgrade to this machine which will equip it with the following features:

the ability to produce pulse sequences involving from 1 to 4 pulses and 1 to 4 delays, each of independently variable duration; this allows nutation and multi-dimensional pulsed EPR experiments.
the ability to independently cycle the phases of each pulse in a sequence in increments of 90 degrees; this allows for the suppression of instrumental artifacts.
complete software control over all instrumental timing and phase cycling functions; there are no knobs to adjust, so the instrument can be configured precisely and repeatably.
relatively easy addition of more pulses; addition of digital delay generators and straightforward modifications to the software are all that are required.

Examples of experimental techniques now possible with our upgraded machine, and a deeper discussion of their utility, may be found in the following reviews and references cited in loc.

Selected Bibliography

Time Domain Electron Spin Resonance, L. Kevan and R. N. Schwartz, editors. Publisher: John Wiley & Sons - New York, Year: 1979, ISBN: 0-471-03814-8

"Pulsed EPR on Disordered Systems: Novel Experimental Schemes" by A. Schweiger, in Advanced EPR Techniques, Applications in Biology and Biochemistry, A. Hoff, editor. Publisher: Elsevier - Amsterdam, Year: 1989, ISBN: 0-444-88050-X

Modern Pulsed and Continuous Wave Electron Spin Resonance Larry Kevan and Michael K. Bowman, Editors. Publisher, John Wiley & Sons. - New York, Year: 1990, ISBN: 0-471-50274-X

Electron Spin Echo Envelope Modulation (ESEEM) Spectroscopy), Sergei A. Dikanov and Yuri D. Tsvetkov. Publisher: CRC Press, Inc. - Boca Raton, FL, USA, Year: 1992, ISBN: 0-8493-4224-4

Here is a picture of our pulsed S-Band spectrometer.

Here is a low-resolution schematic of the Pulse and Phase Controller we have constructed as a part of the recent upgrade of this machine.

Here is a block diagram of the pulsed S-Band EPR spectrometer.

This page was created by John Chen and Dwight Schwartz (1995)

This is an experimental page and may change without notice.