Application of two-dimensional pulsed EPR nutation spectroscopy to a disordered system with large g-anisotropy

Two-dimensional (2-D) pulsed electron paramagnetic resonance (EPR) nutation spectroscopy is applied to a disordered system with strongly anisotropic g-factors. The analysis and interpretation of a 2-D nutation spectrum is performed by theoretical calculations appropriate for ferric myoglobin cyanide in frozen solution. The observed and calculated 2-D spectra show broad signals which correspond to the principal g-values. The advantage of nutation spectroscopy is demonstrated by measuring the g_x = 0.93 signal, which cannot be observed in a conventional field-swept spectrum due to large g strain broadening. It is shown that the 2-D nutation experiment can be considered as a sort of an angle-selected method but a nutation spectrum gives a powder pattern even for magnetic field settings at extreme field values of an EPR spectrum. This is in contrast to angle-selected electron nuclear double resonance, which gives a single-crystal type spectrum. The advantage of sine Fourier transform (FT) over complex FT is demonstrated for data processing in the nutation domain. Problems of experimental and data-processing procedures are also discussed.