Knowledge Bank

The naphthalene triplet $(T1)$ has been studied using laser induced phosphorescence excitation spectroscopy. The experiment was performed for both naphthalene $–h8$ and naphthalene $–d8$ 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 $–d8$ crystal shows less splitting than the naphthalene $–h8$ 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 $–d8$ crystal. In addition, the naphthalene $–d8$ crystal shows less vibronic intensity, relative to the origin, than the naphthalene $–h8$ crystal.