CXXI. Emmission band spectra of aromatic compounds. Part II.—Their origin

From a consideration of a parallel between the infra-red band intervals of ethylene and the ultra-violet band intervals of benzene, naphthalene, and anthracene, the bands exhibited by these substances are considered to originate in a C=C bond. Similarly the band intervals of type (2) of the preceding paper are shown to originate in a CH bond. Benzene also shows vibrations having this origin, and the spectrum is accounted for as a combination of C=C and CH vibrations. It is considered most probable that the “blue band” type of spectrum originates from a carbonoxygen bond and evidence on this point is brought forward. A view of the benzene molecule ix taken accounting for the fact that the bands originating from the two carbon atoms of the C=C bonds show evidence of their being in a state of mutual rotation, whilst the CH groups appear to have a rotation frequency of which their vibration frequency is an exact multiple. This is necessitated if the symmetry of the molecule is to be preserved.