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Electron Paramagnetic Resonance (EPR) Facility

Electron Paramagnetic Resonance

is a class of spectroscopic techniques based on inducing resonance transitions of electron spins by incident radiofrequency irradiation. The properties of these transitions (e.g., the resonance frequencies or magnetic fields and the transition probabilities) can reveal a great deal of information about the electronic and chemical structure of a system under study. A good online introduction to the principles of EPR can be found on the website of Bruker, the world largest maker of EPR spectrometers. Here are some other sites that offer introductory information on EPR:

We are here to provide a quality support to the research effort of the Faculty of the UA Department of Chemistry and for outside customers. Not only are we able to perform various kinds of EPR experiments, but we also provide an interpretation of the spectroscopic results in terms of chemical, geometrical and electronic structures, and help to describe the EPR results in your publications or reports. So if you have any problems involving paramagnetic centers (transition metal ions, stable or transient radicals), come and talk to us. Together we may come up with interesting projects that will enrich your research and make it even more fun than it already is.

Available Equipment:

Resonators:

Our CW EPR resonators are those from Bruker, and they are not equipped for ENDOR. The pulsed EPR resonators are all homemade, and those for the frequencies higher than 8 GHz have an RF coil for ENDOR. The low-frequency (2 - 8 GHz) resonators are loop-gaps, and they are not equipped for ENDOR.

Timing:

Timing for pulsed EPR spectrometers is provided by AWG1000-DOUT board from Chase Scientific. This board has 12 digital (TTL) outputs with 1 ns time resolution, and it directly controls most of switchable devices (mw switches, phase modulators) in the pulsed spectrometers.

 

Temperature control equipment:

The temperature control equipment includes two cryostats, ESR-900 and CF-935 from Oxford Instruments, coolant (liquid helium or nitrogen) transfer tube, temperature controllers and pumps. With this equipment we can perform CW EPR experiments at temperatures from ~ 4 K to ~ 600 K, and pulsed EPR experiments at temperatures from ~ 3.7 K to ~ 300 K.

ENDOR equipment and possibilities:


Our ENDOR equipment includes two RF synthesizers (PTS-310 and HP8657A) and a power amplifier AR 250L from Amplifier Research. The pulsed ENDOR experiments are currently possible in X/Ku- and Ka bands, which is determined by the fact that only for these bands the ENDOR resonators are currently available in this Facility. Currently we are not equipped for CW ENDOR experiments.

General information:


In addition to usual continuous wave (CW) EPR in X-band we can perform many types of fancy pulsed EPR experiments (ESEEM, ENDOR, ELDOR) at various microwave frequencies from 2 to 40 GHz. Therefore, please contact us in advance in order to discuss your specific needs and schedule your experiments. Although we work with specific types/sizes of sample tubes (see below), it may not be convenient and practicable for you to send your samples to us already in such tubes (a typical example: if you send quartz tubes in dry ice without proper packaging, they will break). Therefore, we will also discuss your options for sending or bringing your samples.

Our current rates:


The instrument time is $16/hr for on-campus customers and $60/hr for out-of-campus customers. In addition, you will have to cover any material expenses related to your experiments (e.g., liquid helium).

Sample tubes:


The size of sample tubes we use depends on the microwave band. For the frequencies of 2 to 18 GHz we use quartz tubes from Wilmad with 4 mm OD, while for Ka-band experiments (26 - 40 GHz) we use quartz tubes with 3 mm OD.

Mail your samples to:
Andrei Astashkin
University of Arizona
Department of Chemistry
1306 E. University Blvd.
Tucson, AZ 85721