Electronic States of p-Benzoquinone. VII. Intensity of the Symmetry-forbidden Electronic Absorption Bands of p-Benzoquinone

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Abstract
The intensity of the symmetry-forbidden electronic absorption band of p-benzoquinone, whose excited states belong to 1B2g, 1Au and 1B1g, has been calculated by the perturbation method. It has been concluded that the absorption band around 2900Å corresponds to the 1B2u←1Ag transition, which is allowed through vibronic interaction with the allowed 1B1g←1Ag transition. The interaction is contributed to almost entirely by b3u C=O bending vibration, whose frequency is 370 cm−1 in the ground state.