THE ULTRAVIOLET ABSORPTION SPECTRA OF METHYL-1,2-BENZANTHRACENES

The ultraviolet absorption spectra of 1,2-benzanthracene, all twelve mono-methyl derivatives, and six dimethyl derivatives have been measured (a) at room temperature in n-heptane solution, (b) at −100 °C. in n-pentane solution. An analysis of the band envelopes indicates that most of the absorption between 33,000 and 25,000 cm. −1 arises from two series of overlapping bands. The members of each series are spaced at intervals of approximately 1400 cm. −1 . The spacing between the two band series and their relative intensities are dependent on the nature and position of the alkyl substituents. Absorption between 40,000 and 33,000 cm. −1 can be treated in a similar manner. Other fine structure is also observed. It is considered most probable that each of the overlapping series of bands is associated with a separate electronic excitation. The significance of these observations is considered in relation to the theoretical treatments of the energy levels of 1,2-benzanthracene as developed by Klevens and Platt and by Moffitt.