Knowledge Bank

The emission spectrum of certain mixed crystals can be used to resolve the misting of compound states and measure the relative weighting of individual molecular $states.1,2$ This will be true when the electronic state inter-molecular mixing is large compared to that for the ground state vibrational levels of the two molecules. It must be further assumed that the vibronic intensity pattern for each molecule can be determined in a separate experiment. The system chosen to demonstrate this method is the p-dichlorobenzene-p-dibromobenzene (DCB-DBB) mixed crystal. This is an ideal system because the triplet states of DCB and DBB are nearly degenerate, their phosphorescence spectra have been studied in detail, and they are thought to form solid solutions at all concentrations. Furthermore, the ground state vibrational levels that are active in their respective spectra are significantly different in frequency. In conclusion, the emission spectrum of mixed crystals is found to show the effects of weak electronic state mixing and can be used to measure the extent of this mixing.