THE $T_{1}$ ABSORPTION AND PHOSPHORE SCENCE OF THE $\alpha$-PHASE AND THE $\gamma$-PHASE OF p-DICHLOROBENZENE

Author Institution: Sterling Chemistry Laboratory, Department of Chemistry, Yale UniversityThe assignment of the $T_{1}$ absorption of p-dichlorobenzene is reevaluated by comparison of the emission and absorption of the $\alpha$-phase of p-dichlorobenzene with the same transitions of the $\gamma$-phase of p-dichlorobenzene, which is the stable phase below $0^{\circ} C$. The phosphorescence of the $\alpha$-phase of p-dichlorobenzene arises primarily from defect sites and exhibits a prominent $b_{2g}, n\times 307$ $cm^{-1}$ progression-forming mode which can be followed through n = 5. The $\gamma$-phase of p-dichlorobenzene exhibits the $n\times 307 b_{2g}$ mode through n = 10 and a $n\times 295 b_{2g}$ progression built on a defect origin. A $94 cm^{-1}$ progression forming-mode of the $T_{1}$ state of the $\gamma$-phase has been assigned to the 307 $b_{2g}$ mode of the ground state. The same progressions can be found in the $T_{1}$ absorption of the $\alpha$-phase although the anharmonicity of the progressions prevented them from being recognized by previous workers who assigned the lines to ungerade fundamentals