Very high frequency (263 GHz) pulse EPR spectroscopy of high spin transition metal centers.

A 263 GHz pulse EPR spectrometer using a new 10 W traveling-wave vacuum tube amplifier enables high signal-to-noise electron spin echoes for high-spin Mn(II) (S=5/2) systems without a resonator.

• Why it matters: Access to pulse EPR above ~100 GHz has been limited by insufficient high-power amplifiers, restricting studies of spin S>1/2 where zero-field splitting broadening dominates at low frequency.
• What they did: The work builds a pulse EPR instrument with a 10 W amplifier and wide bandwidth centered at 263 GHz, then demonstrates performance on Mn(II) complexes from impurities in a diamagnetic host to Mn(II) bound in metal sequestering proteins.
• The result: The available mm-wave power supports resonator-free electron spin echo detection, improving study of high-spin (S=5/2) Mn(II) species where zero-field splitting effects are prominent.

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