Equipment

Purpose:  Establish the presence of paramagnetic centers, assign their chemical origin, and provide the preliminary characterization (e.g., determine the g-factors and strong hyperfine interactions).

Equipment:  Bruker Elexsys E500 CW EPR spectrometer. The spectrometer operates in the microwave X-band (9 - 10 GHz) and Q-band (34 GHz).

Pulsed EPR:

Purpose:  In-depth study of molecular systems containing the paramagnetic centers. The obtainable information includes magnetic relaxation times, weak hyperfine and nuclear quadrupole interactions, distances between paramagnetic centers, etc. The whole range of pulsed EPR techniques is available, including ESEEM in one and two dimensions (e.g., HYSCORE), DEER, and RIDME.

Equipment:  A homebuilt broadband pulsed EPR spectrometer continuously covering the range of microwave frequencies from 2 to 40 GHz, with the exclusion of the band between 18 to 26 GHz. The corresponding microwave bands are S (2 - 4 GHz), C (4 – 8 GHz), X (8 – 12 GHz), Ku (12 – 18 GHz) and Ka (26 – 40 GHz). The microwave power amplifiers from Applied Systems Engineering, Inc. are based on 1 kW TWTs for the 2 – 18 GHz range and ~ 300 W TWT for the 26 – 40 GHz range. This power is sufficient to enable the use of narrow microwave pulses (~ 10 ns) required in ESEEM, DEER, and RIDME experiments.

ENDOR equipment and possibilities:

Purpose:  ENDOR is mostly used to measure weak hyperfine interactions (hfi), but in some cases strong hfi can also be measured. Both CW and pulsed versions of ENDOR are available. The CW ENDOR experiments are performed at X-band, and they are mostly used to determine isotropic hfi constants. The pulsed ENDOR experiments can be performed at Ku or Ka band.

Equipment:  In CW version, the RF is generated by the Bruker DICE ENDOR accessory and amplified by the power amplifier AR 250L (Amplifier Research). In pulsed version, two RF synthesizers (PTS-310 and/or HP8657A) and the same power amplifier are used.

Measurement temperatures:

- Room temperature.
- 77 K (liquid nitrogen boiling point at 1 atm) achieved using a finger dewar.
- Temperatures between ~ 4 K to ~ 400 K achieved using cryogenic gas/liquid (nitrogen, helium) flow systems. Different resonators generally require different flow systems, which results in different specific temperature ranges for different resonators.

Abbreviations:

ESEEM – Electron spin echo envelope modulation
HYSCORE – Hyperfine sublevel correlation
DEER – Double electron – electron resonance
RIDME – Relaxation-induced dipolar modulation enhancement
ENDOR – Electron-nuclear double resonance