ESR spectra of concentrated solutions of manganese(II) perchlorate (1ndash;3.2M) do not indicate strong spin exchange and the dipolemdash;dipole interaction is considered to be the predominant intermolecularhyphen;relaxation process. A model of the ESR spectrum is constructed using 30 Lorentzian distribution functions positioned according to a relation developed by Hurd, Sachs, and Hershberger. Ratios of the second moment for the various electronhyphen;magnetic transitions are used to approximate the linewidth ratios of the transitions and thereby reduce the number of linewidth parameters to one, Dgr;HDfrac12;, the dipolarhyphen;linewidth contribution to the minus;frac12;rarr;frac12; absorption. Dgr;HDfrac12;is calculated from the experimental spectra by trial and error. The variations of Dgr;HDfrac12;with increasing temperature indicates that for concentrations less than 1.9Ma simple rapidhyphen;motion diffusion model is sufficient to explain the narrowing of the spectrum. Above 1.9M,Dgr;HDfrac12;follows a modified exponential function, Dgr;HDfrac12;=ADmdash;BDexp(mdash;u/kT), in whichADvaries linearly with concentration andBDandUare very nearly concentration independent. A weak exchange interaction is suggested for the more concentrated solutions.
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