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

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 a llows one to perform one- and two-dimensional multifrequency pulse EPR and pulse ENDOR experiments, as well as continuous wave experiments. It is equi pped with two microwave sources and four microwave channels to generate pul se sequences with different amplitudes, phases, and carrier frequencies. A microwave pulse power of up to 100 W is available. Two channels form radiof requency pulses with adjustable phases for ENDOR experiments. The spectrome ter performance is demonstrated by single crystal pulse ENDOR experiments o n a copper complex. A HYSCORE experiment demonstrates that the advantages o f 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 i s virtually absent in the HYSCORE experiment at Q-band, matched microwave p ulses 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 shor t pulses, and the broad resonator bandwidth make the spectrometer well suit ed to Fourier transform EPR experiments. (C) 2001 Academic Press.