H-1 NMRD PROFILE AND ESR LINESHAPE CALCULATION FOR AN ISOTROPIC ELECTRON-SPIN SYSTEM WITH S=7 2 - A GENERALIZED MODIFIED SOLOMON-BLOEMBERGEN-MORGAN THEORY FOR NONEXTREME-NARROWING CONDITIONS/

A generalization of the modified Solomon-Bloembergen-Morgan (MSBM) the ory is presented for electron-spin quantum number S = 7/2 taking multi exponential electron-spin relaxation into account. The theoretical app roach closely follows P.-O. Westlund [Mol. Phys. 85, 1165-1178 (1995)] . In the nonextreme-narrowing regime for the electron spin system, thr ee correction terms to the traditional MSBM equations arise. They are all derived in closed analytical form to give the generalized equation s in a simple and convenient form: MSBM x (1 + correction). The ESR li neshape function for S = 7/2 is also given in closed analytical form. A number of proton T-1 NMRD profiles representing different Gd(III) co mplexes are investigated, using a spectral density function of the tra nsient ZFS interaction which allows for two relaxation times. For Gd-m acromolecular complexes the largest deviation from the traditional MSB M theory may be about 15.2%, but for the parameter sets investigated t he corrections were about 2-3%. A computer program is developed which calculates the NMRD profile and the ESR lineshape (X band or Q band) f or the set of model parameters. These parameters describe the electron spin system in terms of Delta, (the root-mean-square value of the tra nsient ZFS interaction) and tau(v1), tau(v2), and S-0 (correlation tim es and an order parameter of the transient ZFS correlation function). For the paramagnetically enhanced nuclear (I = 1/2) spin relaxation, t he parameters tau(R) (the reorientational correlation time), q (the nu mber of fast exchanging water molecules in the first hydration shell), and r(1S) (the point spin-dipole distance) are also used. (C) 1996 ac ademic Press, Inc.