Low Resolution Electronic Spectrum of Crystalline para-Dimethoxybenzene with Application to Benzene

The spectrum of a thin (0.37μ) crystal of para-dimethoxybenzene for light incident on the 001 plane and polarized along the a and b crystallographic axes is given. From this, approximate spectra are determined for the two in-plane directions of the molecule. Absorption at 2900 A is polarized predominately in a direction perpendicular to the line joining the substituents while absorption at 2350 A is parallel to this line. The 2600 and 2000 A absorptions in benzene are related respectively to the 2900 and 2350 A bands in dimethoxybenzene and consequently the benzene bands are found to arise from transition to upper states of species B2u and B1u respectively. The relation to conventional orbital theory is briefly discussed.