Simulation of electron spin resonance spectra by fast fourier transform

A computer program is described for the rapid calculation of solution and polycrystalline electron spin resonance spectra of systems containing one unpaired electron. The calculation time is virtually independent of the number of e.s.r. transitions considered, e.g., morphamquat radical cation (3025 lines) requires 4.5 s. Second-order corrections and line-width anisotropy can be included in the simulation. The graphical output may be matched to the output of any e.s.r. spectrometer. Instrumental parameters, e.g. modulation amplitude and time constant, are accounted for in the calculation of the simulated spectrum which enables exact comparison between experimental and simulated spectra. To accommodate mixtures of paramagnetic species, a spectrum addition facility is provided; the output may be presented as an absorption or as any derivative. Spectra originating from isotopically substituted molecules may be calculated routinely and quickly, without the necessity for prior calculation of the relative contributions of the various combinations of isotopic nuclei. Several examples are given, illustrating the usefulness of this program in extracting spectral information under most experimental conditions