Zero-field electron spin echo envelope modulation spectroscopy

Two-pulse and three-pulse electron spin echo envelope modulation (ESEEM) patterns and pulse ENDOR spectra have been observed at zero magnetic field. It is shown theoretically that for systems with half-integer electron spin quantum numbers optimum conditions for zero-field ESEEM are expected for the observer frequency at an electron spin transition between states with magnetic quantum numbers ms = ±12 and ms = ±32. Furthermore, it is found that a compensation of the earth field is not needed for the measurement of unperturbed nuclear frequencies in the ms = ±32 manifolds. From the three-pulse zero-field ESEEM spectrum of the [MnCl4(H2O)2]2− center in polycrystalline ammonium chloride, hyperfine and nuclear quadrupole couplings of the four nearest neighbour chlorines of the manganese ion have been evaluated.