THE ISOTOPE EFFECT ON EXCITATION EXCHANGE INTERACTIONS IN THE TRIPLET OF CRYSTALLINE NAPHTHALENE

Author Institution: Department of Chemistry, Yale UniversityThe naphthalene triplet $(T_{1})$ has been studied using laser induced phosphorescence excitation spectroscopy. The experiment was performed for both naphthalene $–h_{8}$ and naphthalene $–d_{8}$ crystals at $\cong 15^\circ K$. Analysis shows an isotope effect upon the magnitude of the excitation exchange interaction as measured by the splitting of the Davydov components. We have observed that the naphthalene $–d_{8}$ crystal shows less splitting than the naphthalene $–h_{8}$ crystal. This effect is of comparable magnitude and of the same sign as that observed for the naphthalene singlet $state.^{1}$ It has the opposite sign from what would be expected from the anticipated reduction in intermolecular distances in the $–d_{8}$ crystal. In addition, the naphthalene $–d_{8}$ crystal shows less vibronic intensity, relative to the origin, than the naphthalene $–h_{8}$ crystal