Knowledge Bank

The ultraviolet absorption spectra from 25000 to 46000 ($cm-1$ of benzo [$\alpha$]anthracene and of its 12 monomethyl derivatives were measured in solid hydrocarbon glasses at liquid air temperature. The effects of temperature on the individual bands were studied. The fluorescence spectra at room temperature were also determined. The results obtained, give evidence of the fact that between 26000 and $33000cm-1$ there are two extended overlapping electronic band systems The $\alpha (1Lb\leftarrow 1A)$ hand system does include not only the weak bands between 26000 and $27000cm-1$ but continues much further below the p band system reaching about $31000cm-1$. It if very probable that there are two overlapping electronic band system in the 33000--38000 $cm-1$ region as well and three more electronic band systems from 38000 to $46000cm-1$. The spectrum of the “crowded” molecule 1,12 dimethyl benzo[$\alpha$]anthracene is also presented and discussed.