Subramanya, Manoj Vinayaka Hanabe, Jonathan Marbey, Krishnendu Kundu, Johannes E. McKay, and Stephen Hill. “Broadband Fourier-Transform-Detected EPR at W-Band.” Applied Magnetic Resonance 54, no. 1 (January 1, 2023): 165–81.
https://doi.org/10.1007/s00723-022-01499-3.
We report a true wideband Fourier transform (FT) EPR detection capability at the uniquely high frequency of 94 GHz (W-band). It is based on the quasi-optical HiPER spectrometer developed at the University of St. Andrews, into which we have integrated an arbitrary waveform generator (AWG) that is used to modulate the output from a solid-state multiplier chain prior to amplification, generating up to 1 kW microwave power with 1 GHz instantaneous bandwidth. Benchmark experiments are presented for a standard TEMPOL radical, which comprises a 500 MHz broad EPR spectrum at W-band. Using a single adiabatic chirp pulse, efficient inversion of this spectrum is demonstrated, enabling frequency-dependent studies of the longitudinal magnetization recovery in the time-domain, again via chirp pulse echo detection. From these measurements, an anisotropy in the spin–lattice relaxation time, T1, can be determined with ease for TEMPOL. In addition, we implement the FT detection scheme for multi-dimensional (electron–electron double resonance, or ELDOR) experiments, demonstrating the full capabilities of the HiPER spectrometer. As an example, we present a chirp pulse, FT-detected version of the ELDOR NMR technique for the TEMPOL radical.