Low-Temperature Absorption Spectra of Benzene, Toluene, and Para-Xylene in the Farther Ultraviolet Region

The absorption spectra of the 2100 A and 1850 A transitions of benzene, toluene, and para-xylene show sharp structure at low temperature. The sharp structure of the 1850 A transition shows that it is a π—π type transition, and not a dissociation band. Its correct assignment is 1A1g ← 1E1u, with analogous assignments in toluene and para-xylene. The 2100 A transitions of these molecules can be assigned to 1A1g ← 1B1u and its analogs, while the 2600 A transitions are assigned to 1A1g ← 1B2u. Evidence presented indicates that there is no 1A1g ← 1E2g transition in this region of the spectrum.