Er 4112 hv

All EPR measurements were performed on a Bruker Elexsys E580 X-band spectrometer equipped with a SuperX-FT microwave bridge. CW EPR measurements were performed using an ER 4122 SHQE SuperX high-sensitivity cavity in combination with an ER 4112-HV Oxford Instruments variable temperature liquid helium flow cryostat. For pulse EPR/DEER measurements, a Bruker EN 4118X-MD4 dielectric ENDOR resonator was used in concert with an Oxford CF935 helium flow cryostat. Microwave pulses generated by the microwave bridge were amplified by a 1 kW traveling wave tube (TWT) amplifier (Applied Systems Engineering, model 117×). The field-swept EPR spectra were obtained using a 2-pulse Hahn echo sequence with a π-pulse of 24 ns and τ of 212 ns. The following 4-pulse sequence^{45 (link)} was used to perform DEER measurements: [π/2] − τ − [π] − t₁ − [ELDOR] − t₂ − [π], where t(π/2) = 12 ns, t(π) = 24ns, τ = 400 ns, t_1,start = 200 ns, t(ELDOR) = 32 ns, t_2,start = 3.5 µs, t(step) = 28 ns. The shot repetition rate was 50 ms with 20 shots per point, averaged for ~600 scans. DEER results were obtained by applying the pump pulse to the Mn(III)/Fe(III) signal and observing on the N• signal. The inverse was also attempted, and found not to significantly alter data quality.