Nuclear modulation of the electron spin echo envelope in glassy materials

Abstract

We have made experimental studies and computer simulations of the nuclear modulation effect in electron spin echoes for a number of frozen solutions in which paramagnetic ions from the 3d and 4f groups are coordinated with hydrogen- and deuterium-containing ligands. The aim was to discover to what extent electron spin echo measurements can be used to characterize the nuclear environment and to find the radial distances of the nearer nuclei for paramagnetic complexes embedded in glassy matrices. The method is easiest to apply for protons and yields information regarding the radial distribution of the nuclei as well as the distances of the nearest neighbors. According to the theory of the modulation effect, the same results and the same modulation depths are to be expected for all I=1/2 nuclei. The method can also be used where the coordinating nuclei are deuterons, but errors introduced by the quadrupolar interaction lead to uncertainties ?12% in the measurement of the radial distance. Deuteron interactions are easily seen against a proton background since the period is quite distinct, and the modulation pattern is deeper. It is shown that in the limiting case of small quadrupolar interactions the modulation depth parameter is proportional to I (I+1).