Paramagnetic resonance in triplet naphthalene at liquid helium temperatures

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Abstract
In order to determine the absolute signs of the zero field splittings of the photo-excited triplet state of dilute naphthalene in durene, we have made electron spin resonance measurements at 4·2°k and 1·65°k, where Boltzmann populations differ sufficiently to cause measurable intensity effects. Our results confirm the theoretical predictions: Z is negative; X and Y are positive. We have also measured decay times of the triplet state at helium temperatures and have found no marked departure from the behaviour at 77°k. We have observed some further resolution in the hyperfine structure at 1·65°k.