Measurements have been made of the absolute intensity of the lowest‐energy electronic state of perylene. The intensities of the Au and Bu factor group states have been found to deviate from an oriented gas model to such an extent that the model proves valueless in this case. The perturbation treatment of crystal‐induced intensity stealing has been very briefly reviewed to examine the effect of the orientation of molecules on the relative importance of second‐order terms. It has been shown that these terms can be responsible for most of the intensity when the active molecular axis is very nearly 90° to the crystal symmetry axis. Numerical values have been obtained for the influence of five higher‐energy states on the intensity of the lowest state. The oriented gas polarization ratio is Ia/Ib=344: 1; the observed value is 1:1.76; the calculated value is 1: 2.05. The calculated and experimental values of the absolute a and b polarized intensity are in fair agreement.The observed splitting (5250 cm—1) between...
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