A Q-band pulse EPR/ENDOR spectrometer and the implementation of advanced one- and two-dimensional pulse EPR methodology.

Abstract

A versatile high-power pulse Q-band EPR spectrometer operating at 34.5--35.5 GHz and in a temperature range of 4--300 K is described. The spectrometer allows one to perform one- and two-dimensional multifrequency pulse EPR and pulse ENDOR experiments, as well as continuous wave experiments. It is equipped with two microwave sources and four microwave channels to generate pulse sequences with different amplitudes, phases, and carrier frequencies. A microwave pulse power of up to 100 W is available. Two channels form radiofrequency pulses with adjustable phases for ENDOR experiments. The spectrometer performance is demonstrated by single crystal pulse ENDOR experiments on a copper complex. A HYSCORE experiment demonstrates that the advantages of high-field EPR and correlation spectroscopy can be combined and exploited at Q-band. Furthermore, we illustrate how this combination can be used in cases where the HYSCORE experiment is no longer effective at 35 GHz because of the shallow modulation depth. Even in cases where the echo modulation is virtually absent in the HYSCORE experiment at Q-band, matched microwave pulses allow one to get HYSCORE spectra with a signal-to-noise ratio as good as at X-band. Finally, it is shown that the high microwave power, the short pulses, and the broad resonator bandwidth make the spectrometer well suited to Fourier transform EPR experiments.