Paramagnetic resonance in phosphorescent aromatic hydrocarbons

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Abstract
Electron paramagnetic resonance spectra are given of glassy solutions of triphenylene, 1, 3, 5-triphenylbenzene, coronene and naphthalene excited into their lowest triplet state by ultra-violet irradiation at liquid-nitrogen temperature. For each substance two spectra were measured: one with the r.f. magnetic field parallel to the constant field, the other with the fields at right angles. A method is suggested for analysing the spectra of those molecules having a trigonal symmetry axis and values of the zero-field splitting parameter are derived. A complete treatment for molecules of lower symmetry has not been given, but it is shown that our results on a glassy solution of naphthalene are in agreement with those obtained by Hutchison and Mangum with single crystals.