Knowledge Bank

High resolution absorption spectra of $ReF6$ in pure and mixed crystals ($MoF6$, $WF6$, $UF6$) have been obtained for the near IR transitions corresponding to the gas phase A $E_{5}/2g \leftarrow $X $G3/2g$ electronic system. The vibronic structure is surprisingly different within the isostructural series of hosts. The 0 - 0 band of the pure crystal is not readily interpretable in terms of the usual Davydov exciton theory. Concentration dependent structure has been observed around the electronic and vibronic origins in the mixed crystals. The guest-guest structure and pure crystal origin seem explicable in terms of magnetic interactions.