Pulse EPR spectroscopy provides powerful tools for examining species with unpaired electrons, such as organic radicals and metal ions, in a wide variety of interesting systems. However, the lack of high-power pulse amplifiers above approximately 100 GHz has limited its applicability at very high frequencies and magnetic fields. Here we describe the use of a new high frequency traveling wave vacuum tube amplifier employed in a pulse EPR spectrometer operating over a wide frequency bandwidth centered at 263 GHz. This novel instrument provides significant improvements in sensitivity and resolution when compared to lower frequency instruments. Very high frequency pulse EPR is of particular utility for studying spin S>1/2 species, given that large broadening effects of "zero-field splitting'' interactions often dominate EPR spectra obtained at low frequency. Improvements obtained at 263 GHz are illustrated for a series of high spin (S=5/2) Mn(II) complexes.
Bio: R. David Britt is the Winston Ko Chair in Science Leadership and a Distinguished Professor of Chemistry at the University of California, Davis. He has been on the UC Davis faculty since 1989 and leads pioneering research in electron paramagnetic resonance (EPR) spectroscopy to unravel the structure and function of biologically important enzymes, especially those involved in photosynthesis and bioenergy such as the oxygen-evolving complex of Photosystem II and hydrogen-producing hydrogenases. Britt’s lab also operates the CalEPR center, one of the largest EPR facilities on the U.S. West Coast. He earned his B.S. from North Carolina State University and his M.S. and Ph.D. from UC Berkeley. Recognized internationally, Britt is a Fellow of both the American Association for the Advancement of Science and the Royal Society of Chemistry and has received major awards including the Royal Society of Chemistry’s Bioinorganic Chemistry Award and the Bruker Prize. He was elected to the American Academy of Arts and Sciences in 2023.