Conventional EPR spectra were obtained at room temperature with a Bruker ESP 380E spectrometer operating at a modulation amplitude of 0.01 mT, with the output microwave (MW) power of 100 mW, the MW attenuation set up to 25 dB and the sweep and constant times of 60 s and 46 ms, respectively. A Bruker ER 4118 X-MD-5 dielectric resonator was used. In pulsed EPR studies, an X-band Bruker ELEXSYS E580 EPR spectrometer was used equipped with a split-ring Bruker ER 4118 X-MS-3 resonator and an Oxford Instruments CF-935 cryostat.
The three-pulse ESEEM sequence (π/2)-τ-(π/2)-t-(π/2)-τ-echo was employed, with excitation at the maximum of the echo-detected EPR spectrum. The pulse lengths were 16 ns and the time delay τ was 204 ns, and the time delay t was scanned from 300 ns to 10 μs, with a 12 or 16 ns time step. The resonator was cooled with a stream of cold nitrogen gas. The temperature was controlled with a nitrogen flow stabilized by a Bruker ER4131VT temperature controller. The sample temperature was kept near 80 K.
The three-pulse ESEEM sequence (π/2)-τ-(π/2)-t-(π/2)-τ-echo was employed, with excitation at the maximum of the echo-detected EPR spectrum. The pulse lengths were 16 ns and the time delay τ was 204 ns, and the time delay t was scanned from 300 ns to 10 μs, with a 12 or 16 ns time step. The resonator was cooled with a stream of cold nitrogen gas. The temperature was controlled with a nitrogen flow stabilized by a Bruker ER4131VT temperature controller. The sample temperature was kept near 80 K.