Excimer fluorescence XII. The pyrene crystal excimer interaction potential

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The excimer fluorescence spectra of pure single pyrene crystals were observed from 4 to 353 °K. The data are analysed to determine the vibrational zero-point energy of the excimer (= 90 cm-1), the force constants of the excited state (= 1.93 x 105dyn/cm) and ground state (= 3.25 x 105dyn/cm) of the dimer, and the equilibrium intermolecular separation (= 3.34 Å) of the excimer. The repulsive intermolecular potential, the excimer energy, and the attractive excimer interaction potential,V'= 51330 - 1.136 x 106/r3(cm-1) are determined as functions of the intermolecular separationr(Å).V'is shown to be consistent with an exciton resonance state originating from the1Bastate of the pyrene molecule.