NON-SECULAR SIMULATION OF FREQUENCY-DOMAIN 2-PULSE POWDER ESEEM SIGNALS IN MULTINUCLEAR SYSTEMS

We have developed a general non-perturbative theory, which simulates t he two-pulse ESEEM signals of disordered solids directly by using the eigenvalues and eigenvectors of the non-secular Liouville superoperato r. The present theory can handle multinuclear systems of arbitrary nuc lear spin quantum number (up to 9/2), systems with rhombic g, hfi (hyp erfine interaction) and nqi (nuclear quadrupole interaction) tensor wi th arbitrary relative orientations and strengths. The simulations pres ented here are for the two-pulse (primary) ESEEM signals under total e xcitation conditions. Non-secular powder simulations at the L-band, an d at lower fields, for large g-tensor anisotropy and/or intermediate h fi differ appreciably from their secular counterparts. Since the high- field approximation for the electron spin is not required in the prese nt theory we can even simulate the echo modulation for strongly couple d, isotropic electron-nuclear systems, and the echo modulation for sys tems with anisotropy only in the g-tensor.