Solvent perturbations in the near-ultraviolet spectrum of benzene

The perturbation band in the 0-0 region of the 2600-A absorption in benzene (the first member of the Ham progression) was measured at room temperature in the solvents carbon tetrachloride, chloroform, dichloromethane, s-tetrachloroethane, methanol, ethanol, ethylene glycol, diethyl ether, dioxan and water. The band was absent in the solvents cyclohexane and n-heptane. The intensity of the band is with two exceptions proportional to the number of oxygen or chlorine atoms per molecule in the solvent, the effect of oxygen and chlorine being about equal. The balance of the frequency and intensity evidence favours its assignment as the 0-0 band of the ¹B _2u ← ¹A _1g transition.