Dipolar Interaction in TEMPAD Biradical. II

Publisher Website
Google Scholar
Abstract
The EPR of TEMPAD single crystals diluted in diamagnetic matrices was studied. The results of the 10% TEMPAD were almost the same as those of the very dilute one studied previously. In the case of the 25% TEMPAD, the spectra are composed of three parts. The central broad line, whose linewidth was analyzed in comparison with the pure TEMPAD case using the three-dimensional Anderson-Weiss formula, is the spectrum of clusters constructed by the free radicals. The side lines with the hyperfine splitting are the spectrum of the isolated TEMPAD molecule, and the outer broad lines are from the molecules coupled in pairs along the a-axis. The EPR spectra of the pure TEMPAD at very low temperature were also measured in order to have information concerning the dipolar interaction in the pure crystal. These spectra are the superposition of the spectra caused by the intra-molecular dipolar interaction and of the spectra due to impurities. All the results were explained with the suitable molecular stack model and the triplet exciton theory.