EPR spectrum of the Fe3+ ion in bromcresol green (C21H14Br4O5S) and features in the dynamics of the surrounding molecules

The EPR spectrum of an Fe3+ impurity in the organic substance bromcresol green (C21H14Br4O5S) is investigated in the temperature interval 4.2–295 K. At a temperature of 4.2 K the spectrum is a superposition of two lines with effective g factors g1=4.39 and g2=2.03. As the temperature is lowered a redistribution of the intensity between line occurs. The integral intensity of the first line decreases with increasing temperature, while that of the second line increases. Another feature of the temperature dependence of the EPR spectrum of the Fe3+ ion in C21H14Br4O5S is manifested in the exponential growth of the width of the second resonance line with decreasing temperature. The observed properties of the EPR spectrum in C21H14Br4O5S are typical for systems with a multiwell potential and permit one to characterize the dynamics of the molecules of the environment of the magnetic ion.