Calculating Slow Motional Magnetic Resonance Spectra

Abstract

In the first volume of Spin Labeling: Theory and Applicationsa chapter was written by one of us (J.H.F.) in which a detailed theory for the interpretation of ESR spectra of spin labels in the slow motional regime (Freed, 1976) was presented. The specific emphasis of that review was on the interpretation of nitroxide spin label spectra and contained many such examples. In the ensuing 13 years, there have been a number of important developments. First and foremost has been the development and implementation of powerful computational algorithms that have been specifically tailored for the solution of these types of problems (Moro and Freed, 1981; Vasavada et al., 1987). The use of these algorithms often leads to more than an order-of-magnitude reduction in computer time for the calculation of any given spectrum as well as a dramatic reduction in computer memory requirements. Concomitant with these improvements in computational methodology has been the revolution in the power and availability of computer hardware. Taken together, these improvements in hardware and software have made it possible to quickly and conveniently perform spectral calculations on small laboratory computers which formerly required the resources of a large mainframe computer. The increase in the available computing power has also made it feasible to incorporate more sophisticated models of molecular structure and dynamics into the line-shape calculation programs.