Itc 502 temperature controller

The cw-EPR measurements were performed at 9.7 GHz using an ELEXYS E680 spectrometer (Bruker, Rheinstetten, Germany) with a rectangular cavity (ER 4102 ST), using a modulation frequency of 100 kHz. For measurements at 120 K, a helium-gas flow cryostat (Oxford Instruments, United Kingdom) with an ITC502 temperature controller (Oxford Instruments, United Kingdom) was used. The frozen samples were inserted in the pre-cooled helium-gas flow cryostat. The EPR spectra were recorded using modulation amplitude of 0.25 mT and a microwave power of 0.63 mW. Typical accumulation times were 10–14 min. No absolute calibration of g values was made. For the simulation a constant shift was applied to the B₀ field to account for the difference between measured B₀ values and the actual B₀ values at the sample.

D-band EPR spectra were obtained on a spectrometer constructed by Smith et al. operating at a fixed microwave frequency of 139.997 GHz.^{37 (link)} Coherent pulses as well as continuous-wave (CW) microwaves are available at a power level of ~100 mW generated by a Virginia Diodes (Charlottesville, VA) active multiple chain (AMC). A silver TE₀₁₁ resonator focusses the microwave field over a sample volume of approximately 200 nL. Echo-detected (ED) EPR spectra were recorded with a Hahn echo sequence: (π/2)_X – τ − (π)_X − τ − echo with 90° pulses of 40 ns and τ = 500 ns using a two-step phase cycle. At each field position 400 shots were acquired with a repetition time of 1 ms. Samples were kept at 80 K using liquid nitrogen, an Oxford Spectrostat CF flow cryostat, and an ITC 502 temperature controller (Oxford Instruments). A Resonance Research (Billerica, MA) field-mapping unit (FMU) measures the ¹H resonance frequency of a water sample placed just below the cryostat in the magnet bore.^{38 (link)}