Computer Simulation of the ESR Spectra of the Naphthalene, Anthracene, and Perylene Radical Cations in a Polycrystalline Medium

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Abstract
Computer simulation of ESR spectra in polycrystalline environments is extended to the case of free radicals in which the unpaired spin is extensively delocalized. An approximate model is proposed for the anisotropic effects (g tensor, dipolar hyperfine tensor, component shape and width). This model is tested on the spectra of anthracene and perylene radical cations in boric-acid glass [G. Vincow and P. M. Johnson, J. Chem. Phys. 39, 1143 (1963)]. The spectral structure is reproduced by the calculations. A principal application of this simulation procedure is the extraction of values of the Fermi contact hyperfine splittings in cases for which these have not been measured. As an illustration, the powder spectrum of the naphthalene cation radical is considered, yielding | a1H | = 5.4 ± 0.3 G and | a2H | = 1.62 ± 0.3 G. In addition calculations are performed which indicate the sensitivity of the simulated spectra to variations in values of the parameters of the model.